Not promising zero? Less than zero? Just about zero? (7)

I believe the answer is:

ominous

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'not promising zero? less than' is the definition.
I can't judge whether this definition defines the answer.

'zero? just about zero?' is the wordplay.
'just' becomes 'minus' (I can't justify this - if you can you should believe this answer much more).
'about' means one lot of letters goes inside another.
'minus' going around 'o' is 'minous'.
'o'+'minous'='OMINOUS'

Can you help me to learn more?

(Other definitions for ominous that I've seen before include "'Sinister, baleful (7)'" , "Threatening, not looking good" , "Minatory, trouble coming" , "Portending evil" , "Looking like trouble coming" .)

I've seen this clue in the Sydney Morning Herald.

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