Thesaurus / synonyms / antonyms / similar words / rhymes / Datamuse / paraphrasing / query expansion. Returns related words for a given input word, configurable across five modes: 'synonyms' (rel_syn), 'antonyms' (rel_ant), 'sounds_like' (homophones / rhymes), 'similar_meaning' (semantically near), or 'related' (commonly co-occurring triggers). Wraps the public Datamuse API — no auth, commercial-OK.