Old wife permitted young bird (5)
I believe the answer is:
owlet
'young bird' is the definition.
(I've seen this before)
'old wife permitted' is the wordplay.
'old' becomes 'o' (abbreviation).
'wife' becomes 'w' (abbreviation).
'permitted' becomes 'let' (to let something happen is to permit it).
'o'+'w'+'let'='OWLET'
(Other definitions for owlet that I've seen before include "Small hooter" , "One may give a little screech" , "Baby nocturnal raptor" , "Baby bird of prey" , "who'll give a hoot?" .)