one-and-only

The phrase "one and only" is a modern English idiomatic intensifier, a classic example of lexicalization where a common syntactic phrase solidifies into a fixed unit with a specialized meaning. Its components are deeply rooted in the Germanic layer of English: "one" derives from Proto-Germanic ainaz, carrying the core sense of singularity, while "only" evolved from Old English "ānlīc" ("one-like"), itself a compound reinforcing the idea of uniqueness. The logic of the phrase is tautological and emphatic, combining "one" (a single entity) with "and only" (exclusively that single entity) to create a powerful rhetorical device that elevates its referent from merely singular to uniquely special and irreplaceable, often used in romantic or celebratory contexts.

This is a hyphenated compound phrase. It is not a single morpheme but a fixed idiomatic expression formed from common English words: 'one' (from Old English 'ān'), 'and' (from Old English 'and'), and 'only' (from Old English 'ānlīc', meaning "one-like").