(1) The part of a hammerhead opposite the flat striking surface (may have various shapes)
WiktionaryText
Etymology
Etymology uncertain. Possibly from panne, pene, (whence Modern French panne "peen"); possibly from a Scandinavian source, cf. dialectal Norwegian penn "peen" or Danish pind "peg".
Verb
To flatten the end of something, especially a rivet, by striking it with a hammer.
