A dog upset at a snail? (8)
I believe the answer is:
alsatian
'a dog' is the definition.
(I know that Alsatian is a type of dog)
'upset at a snail?' is the wordplay.
'upset' indicates an anagram.
'at'+'a'+'snail'='atasnail'
'atasnail' anagrammed gives 'ALSATIAN'.
(Other definitions for alsatian that I've seen before include "Large dog and person from northern France" , "Strong dog known as German Shepherd" , "Large dog and someone from northern France" , "Large canine, may be police dog" , "Large dog and someone from Alsace" .)