quirk / kwərk/ • n. 1. a peculiar behavioral habit: his distaste for travel is an endearing quirk. ∎  a strange chance occurrence: a strange quirk of fate had led her to working for Nathan. ∎  a sudden twist, turn, or curve: wry humor put a slight quirk in his mouth. 2. Archit. an acute hollow between convex or other moldings.• v. [intr.] (of a person's mouth or eyebrow) move or twist suddenly, esp. to express surprise or amusement. ∎  [tr.] move or twist (one's mouth or eyebrow) in such a way.DERIVATIVES: quirk·ish adj.ORIGIN: early 16th cent. (as a verb): of unknown origin. The early sense of the noun was ‘subtle verbal twist, quibble,’ later ‘unexpected twist.’

quirk.
1. Small acute-angled channel, groove, or deep indent by which a moulding stands out from its ground, commonly found in Gothic work. Any deep groove separating one moulding from another or from a flat plane or ground. In the latter case a quirk-bead would have a quirk on each or one side so that it would be flush with both planes or one.

2. Reentrant angle, such as a piece taken out of a regular figure. A rectangular room with a corner boxed in for e.g. a staircase would be classed as having a quirk.

3. Quarrel (1).

quirk verbal trick or subtlety XVI; sudden turn or twist XVII. of unkn. orig.