There's nothing in turning left (3)
I believe the answer is:
'there's nothing' is the definition.
(I've seen this before)
'in turning left' is the wordplay.
'turning' says the letters should be written in reverse.
'left' becomes 'L' (common abbreviation).
'in' written backwards gives 'ni'.
(Other definitions for nil that I've seen before include "Don't despair - . . . desperandum" , "Nothing, no score" , "You get nothing" , "Zero, no score" , "Nothing, zilch" .)