Crossword Genius

An opener of note (3)

Ross

I believe the answer is:

key

This clue is a double definition.

'an opener' is the first definition.
(keys open things)

'note' is the second definition.
(thesaurus)

'of' acts as a link.

(Other definitions for key that I've seen before include "It opens the door" , "It can open" , "explanation" , "Scale system for music" , "Small island" .)

I've seen this clue in the Evening Standard.
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