Water to some extent absorbs toxic compound (8)
I believe the answer is:
paraquat
'toxic compound' is the definition.
The definition suggests a singular noun which matches the answer.
'water to some extent absorbs' is the wordplay.
I cannot really see how this works, but
'water' could be 'aqua' (I've seen this before) and 'aqua' is found in the answer.
'some' could be 'part' (only part of something) and 'part' is found within the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for paraquat that I've seen before include "Poison" , "Toxic, fast-acting herbicide" , "Trademarked weedkiller" , "Toxic substance" .)