One of an opening pair (5)
I believe the answer is:
hinge
This could be a double definition.
'one of an opening' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'pair' is the second definition.
The definition and answer can be both to do with contact as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for hinge that I've seen before include "Door pivot" , "Device for letting door etc swing" , "Fastening for door etc" , "Key principle" , "Door support" .)