Nasty head, as it were, seen round middle of wen (7)
I believe the answer is:
hateful
'nasty' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for hateful that I've seen before include "Unpleasant" , "repellent" , "Dreadful" , "Loathsome" , "Abhorrent" .)