Dig up doctor having superiority (6)
I believe the answer is:
dredge
'dig up' is the definition.
(thesaurus)
'doctor having superiority' is the wordplay.
'doctor' becomes 'Dr' (synonyms).
'having' says to put letters next to each other.
'superiority' becomes 'edge' (synonyms).
'dr'+'edge'='DREDGE'
(Other definitions for dredge that I've seen before include "Clear out (a waterway)" , "Drag up" , "Dig up mud from river or canal bed" , "Deepen a waterway" , "digging equipment" .)