Dad outside with forest creature (5)
I believe the answer is:
panda
'forest creature' is the definition.
(animal that lives in forests)
'dad outside with' is the wordplay.
'dad' becomes 'pa' (both can mean one's father).
'outside' means one lot of letters goes inside another (some letters go outside others).
'with' becomes 'and'.
'pa' enclosing 'and' is 'PANDA'.
(Other definitions for panda that I've seen before include "Bamboo-eating creature" , "Endangered Chinese mammal" , "Endangered animal" , "Bamboo-eating animal" , "Chinese native" .)