undercut has 3 distinct synonyms spread across 3 of its 10 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.
the material removed by a cut made underneath
the tender meat of the loin muscle on each side of the vertebral column
Synonyms, antonyms and the broader and narrower relations for undercut come from Princeton University’s WordNet. Full sources and licences.
a cut made underneath to remove material
cut away material from the underside of (an object) so as to leave an overhanging portion in relief
cut away the underpart of
“undercut a vein of ore”
strike (the ball) in golf, tennis, or hockey obliquely downward so as to give a backspin or elevation to the shot
cut obliquely into (a tree) below the main cut and on the side toward which the tree will fall