An airborne carrier (6)
I believe the answer is:
pigeon
'an airborne carrier' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
This is all the clue.
Can you help me to learn more?
(Other definitions for pigeon that I've seen before include "Town and woodland bird" , "Dupe" , "Bird with heavy body and short legs" , "birdie" , "See 5" .)