Firm with transport in adversity (8)
I believe the answer is:
hardship
'adversity' is the definition.
(I know that adversity can be written as hardship)
'firm with transport' is the wordplay.
'firm' becomes 'hard' (both can mean durable or strong).
'with' means one lot of letters go next to another.
'transport' becomes 'ship' (ship is a kind of transport).
'hard'+'ship'='HARDSHIP'
'in' is the link.
(Other definitions for hardship that I've seen before include "difficult to take" , "Severe difficulty or suffering" , "Adversity, affliction" , "Adversity, grimness" , "Adversity, suffering" .)