Train retired journalists (7)
I believe the answer is:
express
'train' is the definition.
(express train is a kind of train)
'retired journalists' is the wordplay.
'retired' becomes 'ex' (prefix meaning former or onetime).
'journalists' becomes 'press' (the press can mean the newspaper industry).
'ex'+'press'='EXPRESS'
(Other definitions for express that I've seen before include "Convey; particular; train" , "Speak - fast" , "set forth" , "air" , "Non-stop(ping)" .)