Middle English word foulen comes from Proto-Indo-European *puH-, Proto-Indo-European *pow-, and later Proto-Germanic *bi- (By, at; a general locative prefix.)
| Dictionary entry | Language | Definition |
|---|---|---|
| *puH- | Proto-Indo-European (ine) | |
| *pow- | Proto-Indo-European (ine) | |
| *bi- | Proto-Germanic (gem-pro) | By, at; a general locative prefix. |
| *fūlaz | Proto-Germanic (gem-pro) | Foul, dirty. Rotten. |
| *fūlijaną | Proto-Germanic (gem-pro) | (intransitive) To become foul; rot; decay. |
| *fūlijaną | Proto-Germanic (gem-pro) | (transitive) To befoul; make dirty. |
| fūlian | Old English (ang) | |
| fȳlan | Old English (ang) | |
| foulen | Middle English (enm) |