Non-existent (9)
'non-existent' is the definition.
(I know that non-existent can be written as imaginary)
This is the entire clue.
(Other definitions for imaginary that I've seen before include "Pretend" , "Not based on fact, unreal" , "Fancied" , "Unreal, fanciful" , "Fanciful, notional" .)
'non-existent' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for nil that I've seen before include "0" , "Nothing found in senility" , "Nothing, no value" , "Latin zero" , "Nix, nada, nothing" .)