At best, it may help shade the eyes (4)
I believe the answer is:
peak
'at best' is the definition.
Both the answer and definition are adjectives. Maybe there's a link between them I don't understand?
'it may help shade the eyes' is the wordplay.
I cannot really understand how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is present in the answer.
The remaining letters 'pak' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for peak that I've seen before include "Reach the highest point" , "Sharp pointed summit" , "Apex" , "Acme" , "Part of cap; mountain" .)