Company to start operating a railway as a result (9)
I believe the answer is:
corollary
'a result' is the definition.
(I know that corollary is a type of aftermath)
'company to start operating a railway' is the wordplay.
'company' becomes 'co' (abbreviation).
'to start operating' becomes 'roll' (I am not sure about this - if you are sure you should believe this answer much more).
'railway' becomes 'ry' (abbreviation).
'co'+'roll'+'a'+'ry'='COROLLARY'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for corollary that I've seen before include "Deduction; consequence" , "Proposition that follows logically" , "Direct consequence or result" .)