Use a spade (3)
'use a spade' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dig that I've seen before include "Sly remark; excavate" , "Really like" , "Understand" , "criticism" , "Use a spade" .)
(Other definitions for delve that I've seen before include "Reach down and search" , "Intensively research (into something)" , "Rummage deep (in)" , "Dig up - search" , "Hollow" .)