"Deviant toff" in a Latin translation (10)
I believe the answer is:
tangential
'deviant' is the definition.
'toff in a latin translation' is the wordplay.
'toff' becomes 'gent' (I've seen this in other clues).
'in' is an insertion indicator.
'translation' is an anagram indicator.
'a'+'latin'='alatin'
'alatin' is an anagram of 'tanial'.
'gent' put inside 'tanial' is 'TANGENTIAL'.
(Other definitions for tangential that I've seen before include "Irrelevant" , "Peripheral" .)