杯(bēi) - cup, glass; a cup of, a glass of in Mandarin

杯 (bēi) is the measure word for anything you drink from a cup or a glass. One character covers both, so 一杯水 is a glass of water and 一杯茶 is a cup of tea, and the vessel is left to context.

On its own 杯 is not a normal noun in speech. The cup as an object is 杯子, with the empty suffix that Mandarin adds to bare one syllable nouns. 杯 also names trophies, which is why the World Cup is 世界杯.

The trap is dropping the measure word. English lets you say two coffees; Mandarin cannot. 两咖啡 is broken, and you need 两杯咖啡. The same goes for demonstratives: 这杯 is this glass, while 这咖啡 will make a listener wait for the missing syllable.