Cellar area housing plague victims finally floods (5)
I believe the answer is:
rages
'floods' is the definition.
(rage could historically mean a flood)
'cellar area housing plague victims finally' is the wordplay.
'finally' says to take the final letters.
The final letters of 'cellar area housing plague victims' are 'RAGES'.
(Other definitions for rages that I've seen before include "speaks as Hitler!" , "Fits of temper" , "gives anger vent" , "Passions" , "Storms" .)