One Cup
A Drink, Full, A Lot
adverb, noun, な adjective, の adjective
One cup of liquid is equal to one cup. It could just be a drink, but if you're measuring exactly one cup, it needs to be full to the brim. That's a lot of liquid—so be careful not to spill!
一杯 mainly refers to the amount that fills a container, like a cup, glass, bowl, or even spoon. It can also describe something being "full," such as a full stomach or a theater at capacity (like how a cup is filled to the brim!). Depending on the context, it can also mean "a lot," as fullness implies abundance. When it uses that meaning, you'll also often see it written in just kana (いっぱい).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. Just remember that 一 becomes いっ, and 杯 becomes ぱい.
「ちょっと一杯飲みに行かない？」「いいね。」
"Let’s go for a drink." "Sounds like a plan."
子供の時に「一杯のかけそば」という映画を一度だけ観たことがあります。
When I was a child, I watched a movie called "One Cup of Soba Noodles in Broth" just once.
次年度の予算のことで頭が一杯な状態だったので、その夜は一杯もお酒を飲む気にはなれなかった。
My mind was so full of the following year's budget that I didn't feel like having even one drink that night.