Train one-time journalists (7)
I believe the answer is:
express
'train' is the definition.
(express is a kind of train)
'one-time journalists' is the wordplay.
'one-time' 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 "Put into words - fast" , "Utter; speedy" , "Quickly" , "Squeeze out - speak" , "Quick -- exact" .)