English mohair modifies obsolete Italian mocaiarro, from Arabic mukhayyar. The Arabic word literally means choice.
The selected dictionary says the English form was modified; it does not identify a specific cause for that alteration.
Sources
- Merriam-Webster: mohair
Arabic mukhayyar precedes obsolete Italian mocaiarro and English mohair; the Arabic word is literally choice.
- Nuovo De Mauro · mocaiardo
Meanings of the older forms on the word path.