Gloomy, beset by raging sea, surrender (9)
I believe the answer is:
saturnine
'gloomy' is the definition.
(thesaurus)
'beset by raging sea surrender' is the wordplay.
'beset by' indicates putting letters inside ('beset' could historically mean 'cover').
'raging' indicates anagramming the letters.
'surrender' becomes 'turnin' (as in 'turn in your gun').
'sea' anagrammed gives 'sae'.
'sae' going around 'turnin' is 'SATURNINE'.
(Other definitions for saturnine that I've seen before include "moody" , "dull" , "Gloomy (temperament)" , "offering little amusement" , "Turn in sea makes one gloomy" .)