Crossword Genius

Our first cardinal (3)

Ross

I believe the answer is:

one

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

'cardinal' is the definition.
(a cardinal number)

'our first' is the wordplay.
I cannot quite understand how this works, but
'our first' could be 'o' (1st letter of 'our') and 'o' is found within the answer.
The remaining letters 'ne' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for one that I've seen before include "joke" , "doesn't count for much" , "Unity" , "Half of two" , "Single and undivided" .)

I've seen this clue in The Globe and Mail.
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