An opening to think over (4)
I believe the answer is:
pore
This clue could be a double definition.
'an opening' is the first definition.
(I know that pore is a type of opening)
'think over' is the second definition.
'pore' can be an answer for 'think' (poring is a kind of thinking). I am unsure of the 'over' bit.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for pore that I've seen before include "Small hole" , "Where sweat appears" , "Closely study" , "Minute opening in the skin" , "Rope around the skin-opening" .)