Type of well (8)
I believe the answer is:
artesian
'type of well' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for artesian that I've seen before include "Type of deep well" , "(Well) flowing under natural pressure" , "(Well) fed by pressure" , "A nastier sort of well, oddly" , "Type of well that doesn't need a pump" .)