Half of the population lose the head because it could portend disaster (4)

I believe the answer is:

omen

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'portend disaster' is the definition.
'omen' can be an answer for 'portend' (synonyms). I am unsure of the 'disaster' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for omen that I've seen before include "Warning token" , "Prognostication" , "Harbinger, prophetic sign" , "Portent of things to come" , "Augur" .)

I've seen this clue in The Irish Times.

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