Noun

1. A readiness in performance; aptness at doing something; skill; facility; dexterity.
   • 2005, Plato, Sophist. Translation by Lesley Brown. 254a.

     The sophist runs for conver to the darkness of what is not and attaches himself to it by some knack of his;

2. A petty contrivance; a toy; a plaything; a knickknack.
3. Something performed, or to be done, requiring aptness and dexterity; a trick; a device.

Trivia

• Knack was the winning word at the 8th Scripps National Spelling Bee. http://en.wikipedia.org/wiki/Scripps_National_Spelling_Bee

Verb

1. To crack; to make a sharp, abrupt noise to chink.
2. To speak affectedly.