noun
Refers specifically to the fare for a train ride. 汽車 can imply a steam train or a regular train, but the word is used for train fares in general.
汽車賃は往復でいくらですか。
How much is the train fare for a round trip?
運賃 is a general term for transportation fare (bus, train, etc.), whereas 汽車賃 is specific to trains.
Compound of 汽車 (train) and 賃 (fare). The exact historical derivation is straightforward; the word is formed from its components.