unregretful has 1 distinct synonym spread across 1 of its 1 sense. 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 regretful.
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.
feeling no regret
“was completely unregretful about what had happened”
Synonyms, antonyms and the broader and narrower relations for unregretful come from Princeton University’s WordNet. Full sources and licences.