Pen concealed by Miss Wannamaker (4)
I believe the answer is:
swan
'pen' is the definition.
(pen is a female swan)
'concealed by miss wannamaker' is the wordplay.
'concealed' indicates the answer is hidden within the clue.
'SWAN' can be found hidden inside 'by miss wannamaker'.
(Other definitions for swan that I've seen before include "possibly mute" , "Shakespeare is called The .... of Avon" , "Large, long-necked bird" , "Large water bird" , "black, in 7th" .)