A nastier criminal? Well, sort of (8)
I believe the answer is:
artesian
'well sort of' is the definition.
'artesian' can be an answer for 'well' (I've seen this before). I am not certain of the 'sort of' bit.
'a nastier criminal?' is the wordplay.
'criminal?' indicates an anagram (I've seen 'criminal' mean this).
'nastier' is an anagram of 'rtesian'.
'a'+'rtesian'='ARTESIAN'
Can you help me to learn more?
(Other definitions for artesian that I've seen before include "Type of deep well" , "(Well) fed by pressure" , "A nastier sort of well, oddly" , "This well is bored vertically into the ground" , "Type of well that doesn't need a pump" .)