Onion reaches Latin unio through French. The selected route pairs French oignon with the earlier English spelling oinyon.
Etymonline also describes a direct Latin strand and an earlier Old English borrowing. Those are not extra steps in this French route. The sources differ on first-use dating; the puzzle scores no exact date.
Sources
- Merriam-Webster: onion
Word History gives Latin unio, Anglo-French oignon and the Middle English borrowing.
- Etymonline: onion
The main noun entry supplies oinyon among early English spellings and distinguishes other borrowing strands.
- logeion.uchicago.edu · unio
Meanings of the older forms on the word path.
- Anglo-Norman Dictionary · oignon
Meanings of the older forms on the word path.