baseline has 1 distinct synonym spread across 1 of its 3 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.
an imaginary line or standard by which things are measured or compared
“the established a baseline for the budget”
the back line bounding each end of a tennis or handball court; when serving the server must not step over this line
Synonyms, antonyms and the broader and narrower relations for baseline come from Princeton University’s WordNet. Full sources and licences.
the lines a baseball player must follow while running the bases