Be next to huge robin up in the air (9)
I believe the answer is:
neighbour
'be next to' is the definition.
(neighbour can mean to be next to or adjacent to)
'huge robin up in the air' is the wordplay.
'up in the air' indicates an anagram.
'huge'+'robin'='hugerobin'
'hugerobin' with letters rearranged gives 'NEIGHBOUR'.
(Other definitions for neighbour that I've seen before include "One living close by" , "Fellow human" , "Person who lives next door" , "possibly providing part of watch?" , "One lives near you" .)