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sake cup; cup for alcoholic beverages
counter for cupfuls, bowlfuls, spoonfuls, etc.
counter for boats
counter for octopuses and squid
cup; championship
「杯」 has another reading with different meanings.
疲れた時はお茶を二杯飲んで休憩します。
I drank two cups of tea and rested.
朝食後にコーヒーを三杯も飲んでしまった。
I pour three cups of coffee.
ビールを一杯いかがですかと友人に勧めた。
I asked, how about one cup?