kindly has 6 distinct synonyms spread across 1 of its 3 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 unkindly.
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.
showing or motivated by sympathy and understanding and generosity
“was charitable in his opinions of others”
in a kind manner or out of kindness
“He spoke kindly to the boy”
1 of the 3 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 kindly.
Synonyms, antonyms and the broader and narrower relations for kindly come from Princeton University’s WordNet. Full sources and licences.