What pretentious people put on, hot in transport (7)
I believe the answer is:
airship
'transport' is the definition.
(airship is a kind of transport)
'what pretentious people put on hot' is the wordplay.
'what pretentious people put on' becomes 'airs' (as in 'putting on airs').
'hot' becomes 'hip' (both can mean fashionable or trendy).
'airs'+'hip'='AIRSHIP'
'in' is the link.
(Other definitions for airship that I've seen before include "Lighter-than-air craft" , "High-flyer" , "Conveyance" , "Means of transport" , "need approval from CAA" .)