Look attentively over small opening (4)
I believe the answer is:
pore
'small opening' is the definition.
(I've seen this in another clue)
'look attentively over' is the wordplay.
'look attentively' becomes 'po' (I can't explain this - if you can you should believe this answer much more).
'over' becomes 're'.
'po'+'re'='PORE'
Can you help me to learn more?
(Other definitions for pore that I've seen before include "Look intently" , "Closely study" , "Minute passage in skin" , "Tiny opening in the skin" , "Small hole" .)