The story
- Proto-Germanic*pikkōną
- Proto-West Germanic*pikkōn
- Old English*piccian
- Middle Englishpiken
- Middle Englishpekken
- Middle Englishpekker
- English todaypecker
From Middle English pekker, equivalent to peck (“to pick at something in the manner of a bird”) + -er (“forming agent nouns”).
Etymology from Wiktionary, CC BY-SA 4.0.