Travelling in the heartless train disaster (9)
I believe the answer is:
itinerant
'travelling' is the definition.
(I've seen this before)
'in the heartless train disaster' is the wordplay.
'heartless' means to remove the middle letters.
'disaster' indicates anagramming the letters.
'the' with its centre taken out is 'te'.
'in'+'te'+'train'='intetrain'
'intetrain' with letters rearranged gives 'ITINERANT'.
(Other definitions for itinerant that I've seen before include "Travelling from place to place" , "Rambling" , "Person who moves from place to place" , "Tramp" , "Wandering from place to place" .)