Front of engine stuck in railway bank (4)
I believe the answer is:
rely
'bank' is the definition.
(thesaurus)
'front of engine stuck in railway' is the wordplay.
'front of' suggests taking the first letters.
'stuck in' is an insertion indicator.
'railway' becomes 'rly'.
The first letter of 'engine' is 'e'.
'e' placed inside 'rly' is 'RELY'.
(Other definitions for rely that I've seen before include "Be dependent" , "Be sure" , "Bank (on someone)" , "Depend confidently (on)" , "City with cathedral" .)