What some call Shakespeare's pen, maybe (4)

I believe the answer is:

swan

This clue is a double definition.

'what some call shakespeare's' is the first definition.
(Shakespeare is called the Swan of Avon)

'pen maybe' is the second definition.
(pen is a female swan)

(Other definitions for swan that I've seen before include "Sweet name 8 [OF SHAKESPEARE]" , "Flighty" , "Mute, whooper or Bewick's bird" , "Long-necked water bird" , "possibly mute" .)

I've seen this clue in The Times.

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