Old man outside with forest creature (5)
I believe the answer is:
panda
'forest creature' is the definition.
(animal that lives in forests)
'old man outside with' is the wordplay.
'old man' becomes 'pa' (both can mean someone's father).
'outside' means one lot of letters goes inside another.
'with' becomes 'and'.
'pa' going around 'and' is 'PANDA'.
(Other definitions for panda that I've seen before include "One reluctant to mate" , "One bearlike" , "(a cuddly-looking bear)" , "Black-eyed animal" , "WWF symbol" .)