Bird allowed outside pub (6)
I believe the answer is:
linnet
'bird' is the definition.
(linnet is a kind of bird)
'allowed outside pub' is the wordplay.
'allowed' becomes 'let' (I've seen this before).
'outside' means one lot of letters goes inside another.
'pub' becomes 'inn' (I've seen this before).
'let' placed around 'inn' is 'LINNET'.
(Other definitions for linnet that I've seen before include "Brown-gray kind of finch" , "Member of finch family" , "A singing bird as from Yeats's Innisfree" , "North London terminus" , "Passerine bird" .)