Adult stuck in underground river embarrassed to be beaten (9)
I believe the answer is:
leathered
'be beaten' is the definition.
'adult stuck in underground river embarrassed' is the wordplay.
'adult' becomes 'a' (abbreviation).
'stuck in' means one lot of letters goes inside another.
'underground river' becomes 'lethe' (I've seen this before. I am not sure about the 'underground' bit.).
'embarrassed' becomes 'red' (someone may blush or go red when embarrassed).
'a' placed within 'lethe' is 'leathe'.
'leathe'+'red'='LEATHERED'
'to' is the link.
Can you help me to learn more?
(Other definitions for leathered that I've seen before include "Thrashed with a strap" , "beaten?" .)