Two words that can be interchanged in a context are said to be synonymous relative to that context.

synonym: equivalent word.

Roget 516: meaning; signification, significance; sense, expression; import, purport; force; drift, tenor, spirit, bearing, coloring; scope.    [important part of the meaning] substance; gist, essence, marrow, spirit etc. 5.    matter; subject, subject matter; argument, text, sum and substance.    general meaning, broad meaning, substantial meaning, colloquial meaning, literal meaning, plain meaning, simple meaning, natural meaning, unstrained meaning, true meaning, etc. (exact) 494 honest meaning, etc. 543 prima facie meaning [Lat.]; etc. (manifest) 525.    letter of the law.    literally; after acceptation.    synonym; implication, allusion etc. (latency) 526; suggestion etc. (information) 527; figure of speech etc. 521; acceptation etc. (interpretation) 522.    ... show more

Roget 522: interpretation, definition; explanation, explication; solution, answer; rationale; plain interpretation, simple interpretation, strict interpretation; meaning etc. 516.    translation; rendering, rendition; redition^†; literal translation, free translation; key; secret; clew etc. (indication) 550; clavis^†, crib, pony, trot [U.S.].    exegesis; expounding, exposition; hermeneutics; comment, commentary; inference etc. (deduction) 480; illustration, exemplification; gloss, annotation, scholium^†, note; elucidation, dilucidation^†; eclaircissement [Fr.], mot d'enigme [Fr.].    [methods of interpreting - list] symptomatology [Med.], semiology, semeiology^†, semiotics; metoposcopy^†, physiognomy; paleography etc. (philology) 560; oneirology acception^†, acceptation, acceptance; light, reading, lection, construction, version.    equivalent, equivalent meaning etc. 516; synonym; paraphrase, metaphrase^†; convertible terms, apposition; dictionary etc. 562; polyglot.    ... show more

Dutch: evenwoord, synoniem
Polish: synonim