Rail operated on time (4)
I believe the answer is:
rant
'rail' is the definition.
(thesaurus)
'operated on time' is the wordplay.
'operated' becomes 'ran' ('run' can be a synonym of 'operate').
'on' is a charade indicator (letters next to each other).
'time' becomes 't'.
'ran'+'t'='RANT'
(Other definitions for rant that I've seen before include "Wild speech" , "Angry outburst" , "Intemperate speech" , "Bombastically declaim" , "Talk wildly, rave" .)