Chaps in Regent Street (5)
I believe the answer is:
gents
'chaps' is the definition.
('gent' can be a synonym of 'chap')
'in regent street' is the wordplay.
'in' says the answer is hidden in the clue.
'GENTS' is hidden within 'regent street'.
(Other definitions for gents that I've seen before include "Men (colloq.)" , "toilet" , "Male loos" , "Public convenience" .)