Similar word to quirk:
aberration, caprice, characteristic, conceit, crotchet, eccentricity, equivocation, fancy, fetish, foible, habit, humor, idiosyncrasy, idée fixe, irregularity, kink, knack, mannerism, peculiarity, quibble, singularity, subterfuge, trait, turn, twist, vagary, whim, whimsy
aberration, caprice, characteristic, conceit, crotchet, eccentricity, equivocation, fancy, fetish, foible, habit, humor, idiosyncrasy, idée fixe, irregularity, kink, knack, mannerism, peculiarity, quibble, singularity, subterfuge, trait, turn, twist, vagary, whim, whimsy