Princeton WordNet 3.1 under the WordNet licence, the same database as the Dictionary API, so definitions and synonyms agree.

How are results organised?

By part of speech and then by sense, most common first, so the synonyms for the usual meaning of a word come before those of rare meanings.

Can I get both synonyms and antonyms at once?

Yes. The combined thesaurus endpoint returns both in one response; the separate endpoints return one list each.

What does a call cost?

2 tokens. The free plan covers 250 lookups a month.

DataMAINTAINED2 tokens / call

Thesaurus API

Synonyms and antonyms for English words, grouped by part of speech and ranked by sense, from WordNet 3.1

Synonyms and antonyms for English words, grouped by part of speech and ranked by how common each sense is, from Princeton WordNet 3.1. Ask for synonyms, antonyms or both in one call. Self-hosted, no third-party service.

Every call needs an X-Api-Key header. A free key includes 500 tokens a month, no card required. 2 tokens per call, so the free plan covers about 250 calls a month.

Start free — 500 tokens / mo →See all plans

No credit card requiredAccess to 125+ APIsCancel anytime

response.json

{
  "ok": true,
  "word": "happy",
  "synonym_count": 3,
  "synonyms": {
    "adjective": [
      "felicitous",
      "glad",
      "well-chosen"
    ]
  },
  "antonym_count": 1,
  "antonyms": {
    "adjective": [
      "unhappy"
    ]
  },
  "source": "Princeton WordNet 3.1"
}

Production Ready: Battle-tested infrastructure with a 99.9% uptime SLA. Rate limits are generous, responses are consistent.
Simple Integration: Standard REST + JSON. Works with any HTTP client. Copy-ready code snippets in 4 languages.
One Key, 125+ APIs: Your DataAndAPIs subscription unlocks every API on the platform — anime, finance, sports, and more.

Use cases for Thesaurus API

Suggest alternative words in a writing assistant or editor.
Expand search queries with synonyms to improve recall.
Build word games and vocabulary drills around synonym and antonym pairs.
Normalise tags and keywords by mapping variants to a preferred term.

Thesaurus API endpoints

Every endpoint with its parameters and a real example response.

OpenAPI definition Postman workspace

GETFull Thesaurus
GETGet Antonyms
GETGet Synonyms

GETFull Thesaurus

https://api-thesaurus.dataandapis.com/v1/thesaurus/{word}

Path parameters

Parameter	Example
word	happy	Required

Example request

curl "https://api-thesaurus.dataandapis.com/v1/thesaurus/happy" \
  -H "X-Api-Key: YOUR_API_KEY"

Example response

{
  "ok": true,
  "word": "happy",
  "synonym_count": 3,
  "synonyms": {
    "adjective": [
      "felicitous",
      "glad",
      "well-chosen"
    ]
  },
  "antonym_count": 1,
  "antonyms": {
    "adjective": [
      "unhappy"
    ]
  },
  "source": "Princeton WordNet 3.1"
}

GETGet Antonyms

https://api-thesaurus.dataandapis.com/v1/antonyms/{word}

Path parameters

Parameter	Example
word	happy	Required

Example request

curl "https://api-thesaurus.dataandapis.com/v1/antonyms/happy" \
  -H "X-Api-Key: YOUR_API_KEY"

Example response

{
  "ok": true,
  "word": "happy",
  "antonym_count": 1,
  "antonyms": {
    "adjective": [
      "unhappy"
    ]
  },
  "source": "Princeton WordNet 3.1"
}

GETGet Synonyms

https://api-thesaurus.dataandapis.com/v1/synonyms/{word}

Path parameters

Parameter	Example
word	happy	Required

Query parameters

Parameter	Example
pos	adjective	Optional

Example request

curl "https://api-thesaurus.dataandapis.com/v1/synonyms/happy?pos=adjective" \
  -H "X-Api-Key: YOUR_API_KEY"

Example response

{
  "ok": true,
  "word": "happy",
  "synonym_count": 3,
  "synonyms": {
    "adjective": [
      "felicitous",
      "glad",
      "well-chosen"
    ]
  },
  "source": "Princeton WordNet 3.1"
}

Where the data comes from

Source: Princeton WordNet 3.1, used under the WordNet licence.
Freshness: Static reference data.

One install. Every endpoint.

No proprietary SDKs needed. Any HTTP client works. Pick your language and paste.

3languages

3endpoints

RESTarchitecture

1key for all APIs

Fully typed responses — auto-completion in your IDE
Tracks the API in lockstep — new endpoints land same day
One key works across 125+ APIs on the platform

import axios from 'axios';

const { data } = await axios.get(
  'https://api-thesaurus.dataandapis.com/v1/thesaurus/{word}',
  { headers: { 'X-Api-Key': process.env.API_KEY } }
);

Thesaurus API · X-Api-Key

Explore the endpoints

Browse request parameters and inspect live example responses.

Available Endpoints

Request Parameters

API URL

Headers

X-Api-Key

Path Parameters

word

Target:

Client:

import axios from 'axios';

const url = 'https://api-thesaurus.dataandapis.com/v1/thesaurus/{word}';
const { data } = await axios.get(url, {
  headers: { 'X-Api-Key': 'YOUR_API_KEY' }
});