Tunnel discovered, communist admits very afraid (8)
I believe the answer is:
unnerved
'afraid' is the definition.
(similar in meaning)
'tunnel discovered communist admits very' is the wordplay.
'discovered' means to look at the middle letters (dis-covered - outer letters removed).
'communist' becomes 'red' (red can informally mean communist).
'admits' indicates putting letters inside (to admit is to allow in).
'very' becomes 'v' (common abbreviation).
The centre of 'tunnel' is 'unne'.
'red' going around 'v' is 'rved'.
'unne'+'rved'='UNNERVED'
(Other definitions for unnerved that I've seen before include "Fazed, unsettled" , "Having lost courage or determination" , "scared" , "Deprived of courage or confidence" , "Made someone lose courage or confidence" .)