fret has 22 distinct synonyms spread across 10 of its 16 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
provide (a musical instrument) with frets
“fret a guitar”
an ornamental pattern consisting of repeated vertical and horizontal lines (often in relief)
“there was a simple fret at the top of the walls”
a small bar of metal across the fingerboard of a musical instrument; when the string is stopped by a finger at the metal bar it will produce a note of the desired pitch
Synonyms, antonyms and the broader and narrower relations for fret come from Princeton University’s WordNet. Full sources and licences.