What does "knack" mean?

Additional senses

1. 2.A petty contrivance; a toy; a plaything; a knickknack. A knack, a toy, a trick, a baby's cap. Shak.
2. 3.A readiness in performance; aptness at doing something; skill; facility; dexterity. The fellow . . . has not the knack with his shears. B. Jonson. The dean was famous in his time, And had a kind of knack at rhyme. Swift.
3. 4.Something performed, or to be done, requiring aptness and dexterity; a trick; a device. "The knacks of japers." Chaucer. For how should equal colors do the knack ! Pope.