Where does “汽船” come from?

汽船 (Japanese) comes from Japanese 船, from Old Japanese ふね, from Proto-Japonic punay — boat.

汽船 (Japanese): steamship

Definitions

Step	Language	Word	Meaning
1	Japanese	船	ship, vessel, larger ship
2	Old Japanese	ふね	—
3	Proto-Japonic	punay	boat

汽船 — Etymology, Origin & Word History | Etymology Explorer