Language good and classy in timbre (6)
I believe the answer is:
tongue
'language' is the definition.
(tongue can mean a language)
'good and classy in timbre' is the wordplay.
'good' becomes 'g' (abbreviation).
'and' is a charade indicator (letters next to each other).
'classy' becomes 'u' (I've seen this in other clues).
'in' is an insertion indicator.
'timbre' becomes 'tone' (synonyms).
'g'+'u'='gu'
'gu' going within 'tone' is 'TONGUE'.
(Other definitions for tongue that I've seen before include "cold meat?" , "Flap under shoelaces" , "Language; promontory" , "Go tune up what's in the mouth" , "They are hard to say" .)