Natural consequence of putting Toyota on railway (9)
I believe the answer is:
corollary
'natural consequence of' is the definition.
The definition suggests a singular noun which matches the answer.
'toyota on railway' is the wordplay.
'toyota' becomes 'corolla' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'railway' becomes 'ry' (abbreviation for railway).
'corolla'+'ry'='COROLLARY'
'putting' acts as a link.
Can you help me to learn more?
(Other definitions for corollary that I've seen before include "Proposition that follows logically" , "Direct consequence or result" , "Deduction; consequence" .)