Some left? Yes, of course (9)
I believe the answer is:
certainly
'of course' is the definition.
(I've seen this before)
'some left? yes' is the wordplay.
'some' becomes 'certain' ('certain' can be a synonym of 'some'**).
'left?' becomes 'l' (common abbreviation).
'yes' becomes 'y'.
'certain'+'l'+'y'='CERTAINLY'
(Other definitions for certainly that I've seen before include "Definitely, positively" , "Undoubtedly" , "Without doubt" , "Of course" , "By all means" .)