fast、quick、rapid、swift、hasty、prompt、speedy与instant这些形容词均含有“快速”的意思。
fast : 常指人或物持续地高速运动，强调运动的方式。
fast cars
速度快的汽车
a fast swimmer
速度快的游泳者
Computers are getting faster all the time.
计算机的速度在不断提升。
（拓展学习：熟词僻义 | fast 是一种什么饮食方式？）
quick : 特指瞬时动作，强调动作敏捷迅速；也指匆忙的行为，而不暗示速度很快。
It's a quick journey.
这次行程很短。
I had a quick coffee and left the house.
我匆匆喝完咖啡，离开了家。
I only had time for a quick glance at the paper this morning.
今天早上我的时间只够匆匆浏览一下报纸。
rapid 比 fast 和 quick 正式，常指运动本身，侧重速度惊人。所指动作可能是短暂的，也可能是持续的。
The 1990s were a period of rapid change/growth.
20世纪90年代是一个迅猛突变／发展的时期。
I was startled by a rapid movement to my left.
我左边什么东西猛地动了一下，吓了我一跳。
His response to the accusation was rapid.
他对这种指责马上作出了回应。
swift : 正式用词，强调非常迅速，往往含动作轻快敏捷之意。
The police took swift action against the rioters.
警方对暴动人员迅速采取了行动。
Thank you for your swift reply.
感谢您的即时回复。
The gazelle is one of the swiftest and most graceful of animals.
瞪羚是最敏捷、最优雅的动物之一。
hasty : 多指匆忙、草率或仓促的行动，着重缺乏深思熟虑。
He warned against making hasty decisions.
他警告过不要仓促作出决定。
Now let's not leap to any hasty conclusions.
现在我们不要仓促得出结论。
We saw the rain and made a hasty retreat into the bar.
我们看见下雨了，于是就匆忙躲进酒吧里。
I think perhaps we were a little hasty in judging him.
我认为我们对他的评价可能有点轻率。
prompt : 主要指动作迅速，毫不拖延，含“快得令人愉悦”的意味。
They've written back already - that was a very prompt reply.
他们已经回信了——答复相当迅速。
They're usually fairly prompt in dealing with enquiries.
他们回复咨询通常都比较快。
Try to be prompt because we'll be very short of time.
尽量快点，因为我们时间很紧。
speedy : 指人或物或其运动、活动时，着重极度的快捷，多含匆忙意味。
He's a very speedy worker.
他干起活儿来很麻利。
We need to take speedy action/make a speedy decision.
我们需要迅速采取行动／迅速作出决定。
instant : 指某事很快发生或急待解决，含刻不容缓之意。
In an instant her mood had changed.
顷刻间她的情绪就变了。
The startled boy froze for an instant, then fled.
那个受惊的男孩愣了片刻，然后就逃跑了。