Turgenev regularly leaves on this (4)
I believe the answer is:
tree
'on this' is the definition.
The definition suggests a singular noun which matches the answer.
'turgenev regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'turgenev' are 'TREE'.
'leaves' acts as a link.
Can you help me to learn more?
(Other definitions for tree that I've seen before include "famous actor" , "Diagram representing different relationships" , "''I think that I shall never see / A poem lovely as a ...'' (Kilmer)" , "cross" , "A number" .)