Merriam-Webster Dictionary API
★ Only Publicly Available OpenAPI DocumentData EnrichmentData TransformationapiKey5 EndpointsREST
For Agents
Look up definitions, etymologies, pronunciations, synonyms, and translations across five Merriam-Webster reference dictionaries.
Use for: I need to look up the definition of a word, Find synonyms for a given word, Retrieve a learner-friendly definition for an English learner, Get the medical definition of a clinical term
Not supported: Does not handle full-text search, machine translation of sentences, language detection, or text generation — use for word-level dictionary and thesaurus lookups across the five Merriam-Webster references only.
Jentic publishes the only available OpenAPI specification for Merriam-Webster Dictionary API, keeping it validated and agent-ready. The Merriam-Webster Dictionary API exposes the publisher's reference corpus over HTTP, including the Collegiate Dictionary, Learner's Dictionary, Thesaurus, Medical Dictionary, and Spanish-English Dictionary. Each endpoint takes a word as a path parameter and returns structured JSON containing definitions, etymologies, audio pronunciations, synonyms, and antonyms, suitable for embedding into language tools, study apps, and content-enrichment pipelines.
Install Jentic One Beta
Connect the Merriam-Webster Dictionary API to your agent
Jentic One is a self-hosted execution layer for AI agents. It lets your agent call the Merriam-Webster Dictionary API, or any other public or private API you need. You set the rules, the agent never sees your credentials, and every call is logged.
Two steps, two machines. Install the instance in a safe environment, then register your agent from wherever it runs.
1
Step 1: Jentic One Host machine
# On the machine that will host your Jentic One instance:
curl -fsSL https://raw.githubusercontent.com/jentic/jentic-one/main/tools/install.sh | sh2
Step 2: Agent machine
# On the machine where your agent runs (keep this separate from the instance):
curl -fsSL https://raw.githubusercontent.com/jentic/jentic-one/main/tools/install.sh | sh
jentic register # connects your agent to your Jentic One instanceJentic One is in public beta. The setup above keeps your agent separate from the instance, which is what you want before using real credentials: an agent running as the same OS user as Jentic One can read its stored keys directly. Just evaluating? A single local install is fine to start. See the secure deployment guide for the tiers.
Capabilities
What an agent can do with Merriam-Webster Dictionary API.
Look up a word in the Collegiate Dictionary and return its definitions, parts of speech, and audio pronunciations
Resolve learner-friendly definitions for English-language learners via the Learner's Dictionary endpoint
Retrieve synonyms, antonyms, and related terms for a word from the Thesaurus
Fetch medical-term definitions from the Medical Dictionary for healthcare-adjacent content
Translate and define terms across English and Spanish using the Spanish-English Dictionary
Use Cases
Patterns agents use Merriam-Webster Dictionary API for, with concrete tasks.
★ Vocabulary Study Apps
Language-learning apps can look up words on demand by calling GET /collegiate/json/{word} for general vocabulary or /learners/json/{word} for simplified definitions. The Learner's endpoint surfaces example sentences and audio pronunciations tuned for English learners, which the app can render alongside flashcards.
Call GET /learners/json/serendipity and render the definition, pronunciation audio, and example sentences in the flashcard UI.
Writing Assistant Synonym Lookup
Editorial tools and writing assistants can offer synonym and antonym suggestions by calling GET /thesaurus/json/{word}. The response groups synonyms by sense, so a writing assistant can present meaning-aware alternatives rather than a flat list, which improves suggestion quality for ambiguous words.
Call GET /thesaurus/json/concise and surface the top three synonyms for the user's selected sense.
Medical Content Enrichment
Clinical content platforms can enrich articles and patient-facing materials with Merriam-Webster medical-term definitions via GET /medical/json/{word}. Inline glossaries and tooltips can pull from the API at publish time so that medical jargon is consistently defined across the site.
Call GET /medical/json/anaphylaxis and use the definition as the tooltip text on the article page.
Spanish-English Translation Helper
Bilingual content tools and educator dashboards can translate words between English and Spanish via GET /spanish/json/{word}. The endpoint returns both translations and definitions, which lets the tool show the meaning alongside the translated form rather than a bare lookup.
Call GET /spanish/json/biblioteca and display the English translation plus the example usage in the educator dashboard.
Agent-Driven Word Lookups
An AI agent acting as a writing or research assistant can resolve definitions, synonyms, and translations through Merriam-Webster via Jentic. The agent searches Jentic with the user's intent, picks the right reference (Collegiate, Learner's, Thesaurus, Medical, Spanish), loads the operation, and executes the lookup.
Search Jentic for 'look up a word definition', choose GET /collegiate/json/{word}, and execute it with the user's selected term.
Key Endpoints
5 endpoints — jentic publishes the only available openapi specification for merriam-webster dictionary api, keeping it validated and agent-ready.
METHOD
PATH
DESCRIPTION
GET
/collegiate/json/{word}
Look up a word in the Collegiate Dictionary
GET
/learners/json/{word}
Look up a word in the Learner's Dictionary
GET
/thesaurus/json/{word}
Look up synonyms and antonyms
GET
/medical/json/{word}
Look up a medical term
GET
/spanish/json/{word}
Look up a word in the Spanish-English Dictionary
GET
/collegiate/json/{word}
Look up a word in the Collegiate Dictionary
GET
/learners/json/{word}
Look up a word in the Learner's Dictionary
GET
/thesaurus/json/{word}
Look up synonyms and antonyms
GET
/medical/json/{word}
Look up a medical term
GET
/spanish/json/{word}
Look up a word in the Spanish-English Dictionary
Why Jentic?
Three things that make agents converge on Jentic-routed access.
Credential isolation
Merriam-Webster API keys are stored in the Jentic vault. Agents authenticate with a scoped Jentic token and Jentic appends the key query parameter at the gateway, so the raw API key never enters the agent context.
Intent-based discovery
Agents search Jentic with intents like 'look up a word definition' or 'find synonyms for a word' and receive the matching reference operation (Collegiate, Learner's, Thesaurus, Medical, Spanish) with its parameter schema.
Time to first call
Direct Merriam-Webster integration: half a day to handle key management, reference selection, and response parsing. Through Jentic: under an hour.
Related APIs
Alternatives and complements available in the Jentic catalogue.
FAQs
Specific to using Merriam-Webster Dictionary API through Jentic.
Why is there no official OpenAPI spec for Merriam-Webster Dictionary API?
Merriam-Webster does not publish an OpenAPI specification. Jentic generates and maintains this spec so that AI agents and developers can call Merriam-Webster Dictionary API via structured tooling. It is validated against the live API and kept up to date. Get started at https://app.jentic.com/sign-up.
What authentication does the Merriam-Webster Dictionary API use?
Authentication uses an API key passed as the query parameter named key. Free-tier keys allow 1000 queries per day and access to two reference APIs for non-commercial use. Through Jentic, the key is stored in the credential vault and the agent calls the API with a scoped Jentic token.
Can I look up multiple dictionaries with one Merriam-Webster API key?
The free tier limits a single key to two reference APIs. Commercial subscriptions unlock additional references such as the Medical and Spanish-English dictionaries; the path of each endpoint (/collegiate, /learners, /thesaurus, /medical, /spanish) determines which reference is queried.
What are the rate limits for the Merriam-Webster Dictionary API?
Free-tier keys are capped at 1000 queries per day. Commercial subscriptions raise the daily ceiling and lift the non-commercial-use restriction; high-volume integrations should cache lookups by word and reference to stay well within quota.
How do I look up a word definition through Jentic?
Install the SDK with pip install jentic, search for 'look up a word definition', load the GET /collegiate/json/{word} operation, and execute it with the word as the path parameter. Jentic appends the API key and returns the JSON response.
Does the Merriam-Webster API return audio pronunciations?
Yes. Collegiate and Learner's responses include pronunciation entries that reference audio files served from Merriam-Webster's media host, which clients can resolve to MP3 or WAV URLs for playback in study apps.
GET STARTED