Crossword Genius

Less than a good omen for the millennium? (4)

Ross

I believe the answer is:

dome

I'm a little stuck... Click here to teach me more about this clue!

'the millennium?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'less than a good omen' is the wordplay.
'DOME' is hidden within the letters.
But, I am unsure how this is indicated.

'for' is the link.

Can you help me to learn more?

(Other definitions for dome that I've seen before include "Hemispherical roof" , "Rounded vault of a roof" , "Rounded roof with circular base" , "A stately building" , "Hemispherical structure" .)

I've seen this clue in the Evening Standard.
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