Below-zero greeting? (5)

I believe the answer is:

hello

'greeting?' is the definition.
(hello is a kind of greeting)

'below-zero' is the wordplay.
'below' becomes 'hell'.
'zero' becomes 'o'.
'hell'+'o'='HELLO'

(Other definitions for hello that I've seen before include "Introductory greeting" , "Expression of greeting" , "Hi, howdy" , "opener?" , "Greeting - celebrity magazine" .)

I've seen this clue in The Guardian.

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