Endless increase in dreadfully toxic material (7)
I believe the answer is:
arsenic
This could be a double definition.
'endless increase in' is the first definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'dreadfully toxic material' is the second definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for arsenic that I've seen before include "killer" , "Element with many poisonous compounds" , ", it goes with old lace" , "Toxic metallic element used as rat poison" , "As briefly identified" .)