the part of the head of certain hammers opposite to the flat
striking surface: it is often ball-shaped or wedge-shaped
to hammer, bend, etc. with a peen
Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by
Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'peen'prob. < Scand, as in Norw pænn, sharpened end of a hammer, Swed pæna, to beat out