turnaround has 8 distinct synonyms spread across 4 of its 5 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.
time need to prepare a vessel or ship for a return trip
a decision to reverse an earlier decision
an area sufficiently large for a vehicle to turn around
act or process of unloading and loading and servicing a vessel or aircraft for a return trip
turning in the opposite direction
Synonyms, antonyms and the broader and narrower relations for turnaround come from Princeton University’s WordNet. Full sources and licences.