It reduces toil (3)
I believe the answer is:
oil
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'reduces toil' is the wordplay.
'reduces' means to remove the first letter (I've seen 'reduced' mean this).
'toil' with its initial letter taken away is 'OIL'.
Can you help me to learn more?
(Other definitions for oil that I've seen before include "Type of fuel" , "Viscous substance for lubrication" , "Slippery liquid" , "Liquid fuel" , "Thick liquid that doesn't dissolve in water" .)