Regularly search a pouch (3)
I believe the answer is:
sac
'a pouch' is the definition.
('sac' can be a synonym of 'pouch')
'regularly search' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'search' are 'SAC'.
(Other definitions for sac that I've seen before include "Pouch or bag-like structure" , "pocket" , "Traditional entitlement to hold court" , "Pouch in the body" , "Distended membrane; pouch-like cavity" .)