Crossword Genius

Bar courtesan occasionally lobbing? (4)

Ross

I believe the answer is:

aero

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

'bar' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for aero that I've seen before include "Prefix meaning air or aircraft" , "Prefix denoting air" , "bar" .)

I've seen this clue in the Sydney Morning Herald.
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