to peen is a form of:

Peen



ENGLISH MEANING
noun
1.
A round-edged, or hemispherical, end to the head of a hammer or sledge, used to stretch or bend metal by indentation.
2.
The sharp-edged end of the head of a mason's hammer.
verb
1.
(TRANSITIVE) To draw, bend, or straighten, as metal, by blows with the peen of a hammer or sledge.