Not a straight musician? (7)

I believe the answer is:

fiddler

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'musician?' is the definition.
(fiddler can informally mean a violinist)

I don't understand the remainder of the clue.

(Other definitions for fiddler that I've seen before include "Type of crab; one on the Roof" , "Popular musical '. . . . . . . on the Roof'" , "String player" , "Violinist - swindler - type of crab" , "Musician (on the roof)?" .)

I've seen this clue in The Globe and Mail.

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