Fail to gain a sole option (4)
I believe the answer is:
lose
'fail' is the definition.
(I've seen this in other clues)
'gain a sole option' is the wordplay.
'sole' can be anagrammed to 'LOSE'.
Though, I'm not sure how this is indicated.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for lose that I've seen before include "Fail to keep" , "Shake off (a pursuer)" , "Don't win" , "Mislay or be defeated" , "go down" .)