# Etymonline API

> Etymonline returns English word origins and etymologies, available as a workflow and API.

Etymonline, also called Online Etymology Dictionary, provides word origin entries by part of speech; it needs an English word as input.

- Page: https://fous.com/tools/etymonline
- Handle: `@etymonline`
- Category: [Education](https://fous.com/tools/category/education)
- Source website: https://etymonline.com
- Last verified: Sep 29, 2026

## Methods

### Get word origin

Operation `get_word_origin`, version 1. 1 credit per completed call. Failed calls without a completed billing receipt are free; completed work can remain charged if delivery is interrupted.

Get the origin of an English word, with separate entries by part of speech, the first date mentioned, and linked related words. Dates may be absent for some entries.

**Input**

| Field | Type | Required | Example | Description |
|---|---|---|---|---|
| `word` | string | yes | `"serendipity"` | English word to look up, such as salary. |

**Input schema**

```json
{
  "type": "object",
  "required": [
    "word"
  ],
  "properties": {
    "word": {
      "type": "string",
      "description": "English word to look up, such as salary.",
      "examples": [
        "serendipity",
        "salary"
      ]
    }
  },
  "additionalProperties": false,
  "examples": [
    {
      "word": "serendipity"
    },
    {
      "word": "salary"
    }
  ]
}
```

**Output**

| Field | Type | Example | Description |
|---|---|---|---|
| `entries` | array |  | Origin entries for the requested word, one per listed part of speech. |
| `entries[].heading` | string | `"serendipity (n.)"` | Entry heading as printed on the page. |
| `entries[].entry_link` | string | `"https://www.etymonline.com/word/serendipity"` | Link to this entry on Etymonline. |
| `entries[].earliest_date` | string or null | `"before 20c."` | First date mentioned in the origin explanation, as printed. |
| `entries[].related_entries` | array |  | Words cross-referenced from this origin explanation. |
| `entries[].origin_explanation` | string | `"\"to pay a regular salary to,\" late 15c. (Caxton), from salary (n.). Related: Salaried \"in receipt of a fixed salary\` | Full origin explanation in plain text. |

**Example input**

```json
{
  "word": "serendipity"
}
```

**Example output**

```json
{
  "entries": [
    {
      "heading": "serendipity (n.)",
      "entry_link": "https://www.etymonline.com/word/serendipity",
      "earliest_date": "before 20c.",
      "related_entries": [
        "Sri Lanka"
      ],
      "origin_explanation": "\"faculty of making happy and unexpected discoveries,\" a rare word before 20c., coined by Horace Walpole in a letter to Horace Mann that is dated Jan. 28, 1754, but which apparently was not published u…"
    }
  ]
}
```

## Quick start

Replace `YOUR_API_KEY` with a Fous API key. To create one, open Developers at the bottom of Fous Studio, turn on Developer mode, then go to API keys (https://app.fous.com/keys). Change the values in `input` to run the same tool on new data.

```bash
curl 'https://api.fous.com/v1/query' \
  --fail-with-body --silent --show-error --max-time 180 \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H 'Content-Type: application/json' \
  --data-raw '{
  "api": "@etymonline",
  "visibility": "public",
  "operation": "get_word_origin",
  "version": 1,
  "input": {
    "word": "serendipity"
  },
  "response": {
    "format": "json"
  }
}'
```

```python
# Save as fous.py and run with python3 fous.py. No packages needed.
import json
import urllib.error
import urllib.request

api_key = "YOUR_API_KEY"

body = json.loads("{\n  \"api\": \"@etymonline\",\n  \"visibility\": \"public\",\n  \"operation\": \"get_word_origin\",\n  \"version\": 1,\n  \"input\": {\n    \"word\": \"serendipity\"\n  },\n  \"response\": {\n    \"format\": \"json\"\n  }\n}")
request = urllib.request.Request(
    "https://api.fous.com/v1/query",
    data=json.dumps(body).encode("utf-8"),
    headers={
        "Authorization": f"Bearer {api_key}",
        "Content-Type": "application/json",
    },
    method="POST",
)
try:
    with urllib.request.urlopen(request, timeout=180) as response:
        result = json.load(response)
except urllib.error.HTTPError as error:
    raise RuntimeError(f"HTTP {error.code}: {error.read().decode('utf-8', errors='replace')}") from error
if result.get("success") is False:
    raise RuntimeError(result.get("error", {}).get("message", "Request failed"))
print(json.dumps(result["data"]["output"], indent=2))
```

```typescript
// Save as fous.mts and run with npx tsx fous.mts.
const apiKey = "YOUR_API_KEY";

const response = await fetch("https://api.fous.com/v1/query", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${apiKey}`,
    "Content-Type": "application/json",
  },
  signal: AbortSignal.timeout(180_000),
  body: JSON.stringify({
  "api": "@etymonline",
  "visibility": "public",
  "operation": "get_word_origin",
  "version": 1,
  "input": {
    "word": "serendipity"
  },
  "response": {
    "format": "json"
  }
}),
});
type ApiResult = { success: boolean; data?: { output: unknown }; error?: { message: string } };
const result: ApiResult = await response.json();
if (!response.ok || result.success === false) {
  throw new Error(result.error?.message ?? `HTTP ${response.status}`);
}
if (!result.data) throw new Error("Missing API response data");
console.log(result.data.output);
```

## Use from an AI assistant

Connect this tool to Claude Code, Claude Desktop, Cursor, VS Code, Codex and any MCP client as its own MCP server. Each method is a typed tool whose arguments are the method’s input.

- Server URL: `https://api.fous.com/mcp/tools/etymonline`
- Authorization: `Authorization: Bearer <Fous API key>`

**Tools**

- `get_word_origin`: Get word origin. 1 credit per completed call. Failed calls without a completed billing receipt are free; completed work can remain charged if delivery is interrupted.
- `fous_get_run`: the result of a run that was still going, by its `request_id`. Free.

Claude Code:

```bash
claude mcp add --scope user --transport http fous-etymonline https://api.fous.com/mcp/tools/etymonline --header "Authorization: Bearer ${FOUS_API_KEY:?Set FOUS_API_KEY to your Fous API key}"
```

To give the assistant every tool, connect `https://api.fous.com/mcp`: it finds one with `fous_search_tools` and runs it with `fous_run_tool`. Setup for other clients: https://fous.com/llms-full.txt.

## Use cases

- Trace the origins of English words
- Review the first date mentioned for a word
- Explore related words cross-referenced in an origin entry

## FAQ

### Can I run it with my own inputs?

Yes. Change the inputs in Studio and press Run, or send new inputs from your code, or ask a connected AI assistant.

### Can I call this Etymonline tool as an API?

Yes. Send a POST request to /v1/query with your Fous API key and the inputs, and get JSON back.

### How much does it cost?

Each completed run costs 1 credit. Failed runs without a completed receipt are free; completed work can remain charged if delivery is interrupted. With pay as you go, a credit costs 1¢. Monthly plans cost less per credit.

### Do I need a Etymonline account?

No. You only need a Fous account.

### How current is the data?

Fous gets the data from etymonline.com when you run it. Some results are reused for up to 24 hours, and results that use your account or key are never reused. It was last verified on Sep 29, 2026.

### Where does an English word come from?

Use Get word origin with an English word to retrieve its origin explanation.

### When is a word first mentioned?

Get word origin returns the first date mentioned in each origin entry, when available.

### Which words are related to an origin entry?

Get word origin returns words cross-referenced in the origin explanation.

## Related

- [Dictionary.com API](https://fous.com/tools/dictionary-com.md): Dictionary.com provides definitions, pronunciations, audio, examples, and word origins, plus ranked synonyms and antonyms for public Thesaurus.com entries; some word details may be unavailable.
- [Merriam-Webster API](https://fous.com/tools/merriam-webster.md): Merriam-Webster provides definitions, pronunciations, examples, word histories, synonyms, antonyms, and related words for publicly listed entries, plus Word of the Day entries for today or published archive dates.
- [Wiktionary API](https://fous.com/tools/wiktionary.md): A free, multilingual dictionary with word meanings and language information.
- [Cambridge Dictionary API](https://fous.com/tools/cambridge-dictionary.md): Cambridge Dictionary provides English definitions, examples, grammar labels, and available UK and US pronunciations, plus translations and paired examples for supported languages, reflecting details shown on its pages.
- [Urban Dictionary API](https://fous.com/tools/urban-dictionary.md): Urban Dictionary provides crowdsourced slang definitions and examples, plus up to 30 newest Words of the Day with featured dates.
- [Investopedia API](https://fous.com/tools/investopedia.md): Financial education, investing explanations, and a finance dictionary.
- [WordReference API](https://fous.com/tools/wordreference.md): Dictionary translations and language reference.
- [RhymeZone API](https://fous.com/tools/rhymezone.md): RhymeZone finds rhymes, similar-sounding words, and related words, including synonyms, opposites, descriptions, and associations; some results lack relevance scores or syllable and part-of-speech details.
- [All Education tools](https://fous.com/tools/category/education)