easy has 20 distinct synonyms spread across 8 of its 15 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 2 recorded opposites are difficult, uneasy.
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.
posing no difficulty; requiring little effort
“an easy job”
free from worry or anxiety
“knowing that I had done my best, my mind was easy”
in fortunate circumstances financially; moderately rich
“they were comfortable or even wealthy by some standards”
casual and unrestrained in sexual behavior
“her easy virtue”
5 of the 15 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for easy.
Synonyms, antonyms and the broader and narrower relations for easy come from Princeton University’s WordNet. Full sources and licences.