Descend from bus or train on fire (6)
I believe the answer is:
alight
I believe this is a double definition.
'descend from bus or train' is the first definition.
(I've seen this before)
'on fire' is the second definition.
(synonyms)
(Other definitions for alight that I've seen before include "Get off the bus because it's on fire" , "Come to rest on the ground" , "Get out of train" , "staying in?" , "Settle; on fire" .)