To learn how to do something competently or well after a certain period of practice or development. Wow, you're really getting the knack of playing piano! I've been seeing a tutor to help me with my math homework, and I think I'm starting to get the knack of it.

To be exceptionally proficient at (doing) something. I don't know what it is, but David just has a knack for getting under my skin. Jenny's got a real knack for the piano.

A trinket or bauble, typically one that is small and ornamental. I loved visiting my grandmother when I was a child and examining all the various knick-knacks she'd collected around the house.