Degenerate bore (4)
I believe the answer is:
sink
I believe this is a double definition.
'degenerate' is the first definition.
(thesaurus)
'bore' is the second definition.
(thesaurus)
(Other definitions for sink that I've seen before include "Drop in the ocean?" , "Drop beneath the water - kitchen appliance" , "Plumbing fixture" , "Pocket (billiards)" , "Droop, submerge" .)