sack has 32 distinct synonyms spread across 10 of its 13 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.
a bag made of paper or plastic for holding customer's purchases
any of various light dry strong white wine from Spain and Canary Islands (including sherry)
the plundering of a place by an army or mob; usually involves destruction and slaughter
“the sack of Rome”
the termination of someone's employment (leaving them free to depart)
terminate the employment of; discharge from an office or position
“The boss fired his secretary today”
Synonyms, antonyms and the broader and narrower relations for sack come from Princeton University’s WordNet. Full sources and licences.
put in a sack
“The grocer sacked the onions”