backhand has 4 distinct synonyms spread across 3 of its 4 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 one recorded opposite is forehand.
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.
(of racket strokes) made across the body with back of hand facing direction of stroke
(of handwriting) having the letters slanting backward
a return made with the back of the hand facing the direction of the stroke
Synonyms, antonyms and the broader and narrower relations for backhand come from Princeton University’s WordNet. Full sources and licences.