One waiting in line at an airport (3)
I believe the answer is:
cab
'one waiting in line at an airport' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cab that I've seen before include "Hackney" , "Transport" , "Taxi to hold an engine-driver" , "Driver's compartment, in lorry say" , "vehicle" .)