A catastrophe of old (5)
I believe the answer is:
'a catastrophe' is the definition.
The definition and answer can be both types of natural phenomena as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'of old' is the wordplay.
'of old' can be anagrammed to 'FLOOD'.
However, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for flood that I've seen before include "Inundation" , "lot of water" , "Light" , "Overwhelming amount" , "swamp" .)