The story
- Old French · derived fromoil“eye”
- Old French · derived fromoillet
- Middle English · inherited fromoylet
- English todayeyelet
From Middle English oylet, from Old French oillet, equivalent to Old French oil (“eye”) + -et (diminutive suffix). Spelling and pronunciation were later on influenced by eye (which is distantly related to oil via Proto-Indo-European) as though suffixed with -let (a double diminutive also from -et).
Etymology from Wiktionary, CC BY-SA 4.0.