Young creature always allowed outside (7)
I believe the answer is:
leveret
'young creature' is the definition.
(I've seen this before)
'always allowed outside' is the wordplay.
'always' becomes 'ever' (synonyms).
'allowed' becomes 'let' (to let is to allow or permit).
'outside' is an insertion indicator.
'ever' going into 'let' is 'LEVERET'.
(Other definitions for leveret that I've seen before include "Young creature" , "Young hare" , "Young runner" , "youngster in form" , "Young animal" .)