Impertinent rogue never associated with trial (10)
I believe the answer is:
irrelevant
'impertinent' is the definition.
('irrelevant' can be similar in meaning to 'impertinent')
'rogue never associated with trial' is the wordplay.
'rogue' indicates an anagram.
'associated with' means one lot of letters go next to another.
'never'+'trial'='nevertrial'
'nevertrial' anagrammed gives 'IRRELEVANT'.
(Other definitions for irrelevant that I've seen before include "Impertinent" , "Immaterial" , "Beside the point" , "Not material" , "off-piste?" .)