left-handed has 10 distinct synonyms spread across 3 of its 6 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. Its 2 recorded opposites are ambidextrous, right-handed.
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.
using or intended for the left hand
“left-handed golfers need left-handed clubs”
(of marriages) of a marriage between one of royal or noble birth and one of lower rank; valid but with the understanding that the rank of the inferior remains unchanged and offspring do not succeed to titles or property of the superior
rotating to the left
lacking physical movement skills, especially with the hands
“a bumbling mechanic”
2 of the 6 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for left-handed.
Synonyms, antonyms and the broader and narrower relations for left-handed come from Princeton University’s WordNet. Full sources and licences.