Highly upset by flight? (7)
I believe the answer is:
airsick
'highly' is the definition.
The answer and definition are not the same part of speech.
'upset by flight?' is the wordplay.
'upset' becomes 'sick' (similar in meaning).
'by' means one lot of letters go next to another.
'flight?' becomes 'air' (flight is a kind of air).
'sick' put after 'air' is 'AIRSICK'.
Can you help me to learn more?
(Other definitions for airsick that I've seen before include "Ill when flying" , "Unwell when flying" , "Nauseous in flight" , "Nauseous when flying" .)