Some crabs in thick green liquid (7)
I believe the answer is:
absinth
'liquid' is the definition.
(absinth is a kind of liquid)
'some crabs in thick green' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ABSINTH' is hidden within 'crabs in thick green'.
(Other definitions for absinth that I've seen before include "Potent liqueur, originally made with wormwood" , "Shrubby plant" , "Strong green alcoholic drink" , "Aniseed-flavoured liqueur" , "Strong liqueur with wormwood and anise" .)