Fright when envelope falls off part of airship (3)
I believe the answer is:
car
'part of airship' is the definition.
('car' is part of 'airship')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for car that I've seen before include "Private transport" , "Private vehicle" , "Conveyance" , "Wheels" , "4-wheeled vehicle" .)