grab has 7 distinct synonyms spread across 4 of its 8 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.
make a grasping or snatching motion with the hand
“The passenger grabbed for the oxygen mask”
obtain illegally or unscrupulously
“Grab power”
take or grasp suddenly
“She grabbed the child's hand and ran out of the room”
a mechanical device for gripping an object
the act of catching an object with the hands
“Mays made the catch with his back to the plate”
Synonyms, antonyms and the broader and narrower relations for grab come from Princeton University’s WordNet. Full sources and licences.