Forbidding nothing, and negative about nothing (7)
I believe the answer is:
ominous
'forbidding' is the definition.
('ominous' can be a synonym of 'forbidding')
'nothing and negative about nothing' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'and' is a charade indicator (letters next to each other).
'negative' becomes 'minus' ('minus' can be similar in meaning to 'negative'**).
'about' means one lot of letters goes inside another.
'nothing' becomes 'o' (looks like zero - 0).
'minus' going around 'o' is 'minous'.
'o'+'minous'='OMINOUS'
(Other definitions for ominous that I've seen before include "Sinister-looking" , "Inauspicious" , "Threatening or foreshadowing evil or tragedy" , "'Threatening, foreshadowing tragedy (7)'" , "Threatening disaster" .)