The story
- Proto-Germanic*flataz
- Old Norseflatr
- Middle Englishflat
- Englishflat
- Proto-Indo-European*wed-
- Proto-Indo-European*wodsḱéti
- Proto-Germanic*waskaną
- Proto-West Germanic*waskan
- Old Englishwascan
- Middle Englishwaschen
- Englishwash
- English todayflatwash
Etymology from Wiktionary, CC BY-SA 4.0.