A portentous figure? (3)

I believe the answer is:

ten

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

'figure?' is the definition.
(I've seen this in other clues)

'a portentous' is the wordplay.
'TEN' is hidden within the letters.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for ten that I've seen before include "Half a score" , "PM's address, Downing St" , "Five times two" , "Figure" , "Base of decimal system" .)

I've seen this clue in the Evening Standard.

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