penalty has 3 distinct synonyms spread across 1 of its 4 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 reward.
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 punishing
Synonyms, antonyms and the broader and narrower relations for penalty come from Princeton University’s WordNet. Full sources and licences.
a payment required for not fulfilling a contract
the disadvantage or painful consequences of an action or condition
“neglected his health and paid the penalty”
(games) a handicap or disadvantage that is imposed on a competitor (or a team) for an infraction of the rules of the game