Drone to exist on air (3)
I believe the answer is:
bee
'drone' is the definition.
(I've seen this in another clue)
'exist on air' is the wordplay.
'exist' becomes 'be' (synonyms).
'on air' indicates a 'sounds like' (homophone) clue (how the word sounds on the radio, on air).
'be' sounds like 'BEE'.
'to' acts as a link.
(Other definitions for bee that I've seen before include "Honey-making insect" , "Insect, may be in bonnet" , "Useful insect" , "Buzzing insect" , "meeting" .)