Language - one with a Latin derivation (7)
I believe the answer is:
italian
'language' is the definition.
(Italian is a language)
'one with a latin derivation' is the wordplay.
'one' becomes 'i' (Roman numeral).
'with' means one lot of letters goes inside another.
'derivation' indicates an anagram.
'latin' is an anagram of 'talin'.
'a' inserted within 'talin' is 'talian'.
'i'+'talian'='ITALIAN'
(Other definitions for italian that I've seen before include "South European" , "Native of Sicily, say" , "Romance language" , "Ain't Ali out of Rome, perhaps?" , "European tongue" .)