grounds has 5 distinct synonyms spread across 3 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.
your basis for belief or disbelief; knowledge on which to base belief
“the evidence that smoking causes lung cancer is very compelling”
Synonyms, antonyms and the broader and narrower relations for grounds come from Princeton University’s WordNet. Full sources and licences.
the enclosed land around a house or other building
“it was a small house with almost no yard”
a tract of land cleared for some special purposes (recreation or burial etc.)
a justification for something existing or happening
“he had no cause to complain”
dregs consisting of solid particles (especially of coffee) that form a residue
“it is a Middle Eastern custom to read your future in your coffee grounds”