legitimate has 11 distinct synonyms spread across 3 of its 7 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 illegitimate.
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.
of marriages and offspring; recognized as lawful
based on known statements or events or conditions
“rain was a logical expectation, given the time of year”
make legal
“Marijuana should be legalized”
1 of the 7 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 legitimate.
Synonyms, antonyms and the broader and narrower relations for legitimate come from Princeton University’s WordNet. Full sources and licences.
show or affirm to be just and legitimate
make (an illegitimate child) legitimate; declare the legitimacy of (someone)
“They legitimized their natural child”