1. A male cat, especially a castrated one.
2. A piece of wood or metal designed to hold parts in place or to provide a bearing surface, often adjusted by a screw or key.
Definition 1: Middle English, 'Gib' is a variation of 'Gilbert', and apparently a common name for male cats back in the day.
Shakespeare used it in Henry IV: “I am as melancholy as a gib cat or a lugged bear.”
Definition 2: unknown, from the late 1700s. If you google 'machine gib', numerous examples will be returned.