The story
- Proto-Indo-European*h₁es-
- Proto-Germanic*sunjō
- Proto-West Germanic*sunnju
- Old Englishsynn
- Proto-Indo-European*pleh₁-
- Proto-Indo-European*pl̥h₁nós
- Proto-Germanic*fullaz
- Old Englishsynful
- Middle Englishsynful
- English todaysinful
From Middle English synful, senful, sunful, from Old English synful (“sinful, guilty, wicked, corrupt”), equivalent to sin + -ful. Compare Dutch zondevol (“sinful”), German sündevoll (“sinful”), Danish syndefuld (“sinful”), Swedish syndfull (“sinful”), Icelandic syndfullur (“sinful”).
Etymology from Wiktionary, CC BY-SA 4.0.