One who didn't win the Mountain Race? (6-2)
I believe the answer is:
runner-up
'one who didn't win the mountain' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'race?' is the wordplay.
I cannot really understand how this works, but
'race?' could be 'run' (run is a kind of race) and 'run' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for runner-up that I've seen before include "One coming second" , "Second best?" , "One who is second in a race" , "Silver medallist" , "Second-place" .)