Opening notice, sensitive over grant (5)
I believe the answer is:
award
'grant' is the definition.
(I know that grant can be written as award)
'opening notice sensitive' is the wordplay.
'opening' indicates putting letters inside (some letters open a gap in others).
'notice' becomes 'ad' (both can mean an advertisement).
'sensitive' becomes 'war' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ad' placed around 'war' is 'AWARD'.
'over' is the link.
Can you help me to learn more?
(Other definitions for award that I've seen before include "Adjudge" , "Prize -- gift" , "medal, say" , "Arbitrator's decision" , "Perhaps Tony" .)