Dog Latin as a composition (8)
I believe the answer is:
alsatian
'dog' is the definition.
(alsatian is a kind of dog)
'latin as a composition' is the wordplay.
'composition' indicates an anagram (letters arranged or composed in a different order).
'latin'+'as'+'a'='latinasa'
'latinasa' with letters rearranged gives 'ALSATIAN'.
(Other definitions for alsatian that I've seen before include "Dog (from French border region?)" , "Large dog and someone from Alsace" , "Large dog and person from northern France" , "Large dog and someone from northern France" , "Old Frenchman" .)