decision has 3 distinct synonyms spread across 3 of its 5 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 indecision.
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.
the act of making up your mind about something
“the burden of decision was his”
a position or opinion or judgment reached after consideration
“a decision unfavorable to the opposition”
(boxing) a victory won on points when no knockout has occurred
“had little trouble in taking a unanimous decision over his opponent”
the outcome of a game or contest
“the team dropped three decisions in a row”
the trait of resoluteness as evidenced by firmness of character or purpose
“a man of unusual decisiveness”
Synonyms, antonyms and the broader and narrower relations for decision come from Princeton University’s WordNet. Full sources and licences.