: a usually U-shaped fastener: such as
a : a metal loop both ends of which are driven into a surface to hold the hook, hasp, or bolt of a lock, secure a rope, or fix a wire in place
b : a small wire both ends of which are driven through layers of thin and easily penetrable material (such as paper) and usually clinched to hold the layers together
c : a usually metal surgical fastener used to hold layers of tissue together (as in the closure of an incision)