Example sentences
nǐ你lái来de得zhēn真kuài快。
You came so fast.
kuài快xià下yǔ雨le了。
It's about to rain.
The story behind the character
快
A surprise here. 快 is 忄, the heart, with 夬 for the sound, and Xu Shen defined it 快, 喜也: pleased. The heart radical is the clue. 快 spent its early life meaning happy and delighted. Fast came along later, perhaps from the sense of something pleasing arriving quickly. 快乐 keeps the old meaning.