the act of bending. rounding. or flattening the fastening end of through-hardware for the purpose of preventing a nut from backing off.” “

Merriam-Webster Online Dictionary
peen (verb)
transitive verb
to draw, bend, or flatten by or as if by hammering with a peen
peen (noun)
a usually hemispherical or wedge-shaped end of the head of a hammer that is opposite the face and is used especially for bending, shaping, or cutting the material struck
peen (Wikipedia)

Peen may refer to:

« Back to Glossary Index