Railways ignoring the odds, unfortunately! (4)
I believe the answer is:
alas
'unfortunately' is the definition.
(I've seen this before)
'railways ignoring the odds' is the wordplay.
'ignoring the odds' indicates alternate letters (letters in odd-numbered positions are removed).
The alternating letters of 'railways' are 'ALAS'.
(Other definitions for alas that I've seen before include "Antipodean island state" , "Cry of woe" , "Unhappily" , "woebegone expression" , "Expression of grief or misfortune" .)