1. A peculiarity of behavior; an idiosyncrasy: "Every man had his own quirks and twists" (Harriet Beecher Stowe).

2. An unpredictable or unaccountable act or event; a vagary: a quirk of fate.

3. A sudden sharp turn or twist: a quirk of the head.

4. Architecture A lengthwise groove on a molding between the convex upper part and the soffit.

5. Archaic An equivocation; a quibble.