A crowd, figuratively speaking? (5)

I believe the answer is:

three

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

'a crowd' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

(Other definitions for three that I've seen before include "There (anag.)" , "III" , "Number of Dumas's musketeers" , "... number of his "Steps to Heaven"" , "Cardinal number" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app