1A watercraft used on seas, rivers, etc.; a ship or boat (from large ships to small boats).
大きな貨物船が港に入ってきた。
A large cargo ship entered the port.
夏休みに友達と漁船で沖へ出た。
During summer vacation I went out to sea on a fishing boat with friends.
小さな舟で川を渡った。
We crossed the river in a small boat.
2A tub, vat, or tank used to hold liquids — a specialized, old-fashioned term (e.g. in traditional sake brewing) rarely encountered in everyday modern speech.
酒を発酵させるための木の槽が蔵に並んでいる。
Wooden vats for fermenting sake stand in the brewery.
3A counter/suffix for boat-shaped containers (e.g., servings of sashimi served in a small wooden boat).
刺身を一舟お願いします。
I'd like one boat (serving) of sashimi, please.
パーティー用に海鮮盛りを二舟注文した。
I ordered two boat-shaped platters of seafood for the party.