tactful 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 tactless.
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.
having or showing a sense of what is fitting and considerate in dealing with others
“she was tactful enough not to shatter his illusion”
showing skill and sensitivity in dealing with people
“by diplomatic conduct he avoided antagonizing anyone”
Synonyms, antonyms and the broader and narrower relations for tactful come from Princeton University’s WordNet. Full sources and licences.