Summit closes on attempt to concur (3)
I believe the answer is:
tor
'summit' is the definition.
(thesaurus)
'closes on attempt to concur' is the wordplay.
I cannot really see how this works, but
'on' could be 'to' and 'to' is located in the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tor that I've seen before include "(Dartmoor) rocky hill" , "Rot on a Cornish hill" , "Rocky outcrop" , "Pillar of rock" , "eminence" .)