Originally so jaunty, King Edward’s first dog (10)
I believe the answer is:
'dog' is the definition.
(schipperke is a kind of dog)
'originally so jaunty king edward's first' is the wordplay.
'originally' suggests taking the first letters.
'jaunty' becomes 'chipper' ('chipper' can be a synonym of 'jaunty'**).
'first' indicates taking the first letters.
The initial letter of 'so' is 's'.
The first letters of 'king edwards' is 'ke'.
(Another definition for schipperke that I've seen is " dog".)