vt to fasten with a cotter.
2. cotter ·noun a toggle.
3. cotter ·noun ·alt. of cottar.
4. cotter ·noun a piece of wood or metal, commonly wedge-shaped, used for fastening together parts of a machine or structure. it is driven into an opening through one or all of the parts. [see illust.] in the united states a cotter is commonly called a key.