From 16th-century English, originally meaning a clever trick or device, likely related to Low German 'knack' (a snap or crack), suggesting something done with a sharp, practiced ease. The sense of "a special skill" emerged by the 17th century.

Widely used in both American and British English. Note that "knack" always carries a sense of effortlessness — saying someone has a knack implies the skill comes naturally, not through hard study. It's commonly used as a compliment in casual conversation.