An eyesore — seen in nasty environment (4)
I believe the answer is:
stye
'an eyesore' is the definition.
(I've seen this before)
'in nasty environment' is the wordplay.
'in' says the answer is hidden in the clue.
'STYE' can be found hidden inside 'nasty environment'.
'aeur seen' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stye that I've seen before include "Climb" , "Viewer's complaint" , "Eyelid infection" , "irritation to the viewer" , "Inflammation on eyelid" .)