Synonyms for freak

noun

1. A caprice

   vagary, whim, crotchet; see fancy 3, impulse 2.

2. An abnormal or odd person or thing

   monstrosity, monster, aberration, oddity, abnormality, rarity, anomaly, malformation, mutation, mutant, lusus naturae (Latin), grotesquerie, abortion, freak of nature, curiosity, rara avis (Latin), misfit, queer fish, black swan, sport, hybrid, mooncalf, changeling.