Criminal cross — it's nicer outside (9)
I believe the answer is:
extrinsic
'outside' is the definition.
(similar in meaning)
'criminal cross it's nicer' is the wordplay.
'criminal' is an anagram indicator.
'cross' becomes 'x' (an X is a cross).
'x'+'its'+'nicer'='xitsnicer'
'xitsnicer' with letters rearranged gives 'EXTRINSIC'.
(Other definitions for extrinsic that I've seen before include "What's inessential" , "Not essential or inherent" , "Foreign" .)