Transport not fully occupied (3)
I believe the answer is:
bus
'transport' is the definition.
(I know that bus is a type of transport)
'not fully occupied' is the wordplay.
'not fully' means to remove the last letter.
'occupied' becomes 'busy' (similar in meaning).
'busy' with its last letter removed is 'BUS'.
(Other definitions for bus that I've seen before include "Public transport vehicle" , "Of projectiles; (go) mad (slang)" , "Something caught" , "eg Double-decker" , "Public service vehicle" .)