Momentous things are threat somehow (5-10)

I believe the answer is:

earth-shattering

'momentous' is the definition.
(I've seen this before)

'things are threat somehow' is the wordplay.
'somehow' indicates an anagram.
'things'+'are'+'threat'='thingsarethreat'
'thingsarethreat' is an anagram of 'EARTH-SHATTERING'.

I've seen this clue in The Times.

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