Where does “Merlin” come from?

Merlin comes from Old French Merlin, of unknown ultimate origin.

Ancestry of “Merlin”, step by step

Step	Language	Word	Meaning
1	Middle English	merlioun	—
2	Old French	emerillon	—
3	Old French	esmerillon	—
4	Old French	esmeril	—
5	Italian	smeriglio	emery; merlin; Synonym of sparviero
6	Greek	σμερίλιον	—
7	Ancient Greek	σμερί	—
8	Ancient Greek	σμύρις	emery-powder, used by lapidaries

Merlin — Etymology, Origin & Word History | Etymology Explorer