alternate has 13 distinct synonyms spread across 7 of its 10 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 opposite.
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.
reverse (a direction, attitude, or course of action)
occurring by turns; first one and then the other
“alternating feelings of love and hate”
of leaves and branches etc; first on one side and then on the other in two ranks along an axis; not paired
“stems with alternate leaves”
1 of the 10 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for alternate.
Synonyms, antonyms and the broader and narrower relations for alternate come from Princeton University’s WordNet. Full sources and licences.