Blackbird not unknown in Scottish island (4)

I believe the answer is:

coll

I'm a little stuck... Click here to teach me more about this clue!

'scottish island' is the definition.
(Isle of Coll)

I cannot understand how the rest of the clue works.

(Other definitions for coll that I've seen before include "Hebridean island" , "Scottish island" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.