Vesicle in Clancy Street (4)
I believe the answer is:
cyst
'vesicle' is the definition.
(I know that vesicle can be written as cyst)
'in clancy street' is the wordplay.
'in' indicates the answer is hidden within the clue.
'CYST' can be found hidden inside 'clancy street'.
(Other definitions for cyst that I've seen before include "Small sac in body (that may form abnormal lump)" , "Fluid-filled sac (med.)" , "Sac in the body containing liquid secretion" , "Bag-like growth containing diseased matter" , "Abnormal membranous sac" .)