From Middle English *knak* (a trick, a sharp knock), likely borrowed from Low German or Dutch *knack* (a snap, crack). By the 16th century it had shifted from meaning a trick or device to meaning an acquired clever skill, and later an innate talent.

*Knack* is widely used in both American and British English with no major regional meaning difference, making it a safe, versatile word. Watch out for the false friend trap: the silent initial *k* surprises many learners — it is always pronounced simply /næk/. The phrase "get the knack of" (e.g., "once you get the knack of it") is extremely common in everyday speech.