Crossword Genius

One may be dressed up to them - by numbers? (5)

Ross

I believe the answer is:

nines

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

Here is my best explanation:

'numbers?' is the definition.
(nine is a kind of number)

I can't explain the rest of the clue.

Can you help me to learn more?

This clue was last seen in The Globe and Mail