lap has 11 distinct synonyms spread across 8 of its 11 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 upper side of the thighs of a seated person
“he picked up the little girl and plopped her down in his lap”
an area of control or responsibility
“the job fell right in my lap”
the part of a piece of clothing that covers the thighs
“his lap was covered with food stains”
movement once around a course
“he drove an extra lap just for insurance”
lie partly over or alongside of something or of one another
Synonyms, antonyms and the broader and narrower relations for lap come from Princeton University’s WordNet. Full sources and licences.