reassure has 1 distinct synonym spread across 1 of its 2 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 worry.
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.
give or restore confidence in; cause to feel sure or certain
“I reassured him that we were safe”
Synonyms, antonyms and the broader and narrower relations for reassure come from Princeton University’s WordNet. Full sources and licences.