pinning (Noun) — A mutual promise of a couple not to date anyone else; on college campuses it was once signaled by the giving of a fraternity pin.
pinning (Verb) — To hold fast or prevent from moving. ex. "The child was pinned under the fallen tree"
pinning (Verb) — Attach or fasten with pins or as if with pins. ex. "pin the needle to the shirt". "pin the blame on the innocent man"
pinning (Verb) — Pierce with a pin. ex. "pin down the butterfly"
pinning (Verb) — (chess) immobilize a piece.