"快子" (kuài zǐ) is a Chinese term that can be translated as "speedy" or "fast" in Engpsh. In Engpsh, it is pronounced as "kway-zee."

The word "speedy" is derived from the Old Engpsh word "spēde," which means "swiftness" or "haste." It came to be used as an adjective to describe something that moves or happens quickly or swiftly. For example:

"The cheetah is the world's fastest land animal and can run at speeds of up to 75 mph." (中文翻译: "猎豹是世界上最快的陆生动物, 最高时速可达每小时75英里。")
"I need to finish this project as quickly as possible. Can you help me out?" (中文翻译: "我需要尽快完成这个项目。你能帮帮我吗？")

The word "fast" is derived from the Old Engpsh word "fæst," which means "firmly fixed or held" or "not easily moved or parted." It can also be used to describe something that happens quickly or at a high speed. For example:

"The car was going so fast that I couldn't see the driver." (中文翻译: "这辆车开得很快, 以至于我看不见司机。")
"I'm trying to lose weight, so I'm eating fast food less often." (中文翻译: "我想减肥, 所以我不经常吃快餐。")