A lot of water in case, as pain spreads (7,3)
I believe the answer is:
caspian sea
'a lot of water' is the definition.
I can't judge whether this defines the answer.
'case as pain spreads' is the wordplay.
'spreads' indicates anagramming the letters (I've seen 'spreading of' mean this).
'case'+'as'+'pain'='caseaspain'
'caseaspain' anagrammed gives 'CASPIAN SEA'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for caspian sea that I've seen before include "World's largest inland body of water, fed by the Volga River" , "World's largest lake" , "There's lots of water here" , "Lake bordered by both Russia and Iran" , "Largest salt lake in the world" .)