Crossword Genius

By which to travel from Cairo? (3)

Ross

I believe the answer is:

air

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

'by which to travel' is the definition.
I can't tell whether this defines the answer.

'from cairo?' is the wordplay.
'from' says the answer is hidden in the clue.
'AIR' is hidden within 'cairo'.

Can you help me to learn more?

(Other definitions for air that I've seen before include "Atmosphere (of a melody?)" , "Carriage" , "what emerges from singer's lungs?" , "Divulge" , "Spread publicity" .)

I've seen this clue in the Evening Standard.
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