快 literally means fast, quick, rapid, swift, and speedy. However, it has other meanings.
It can mean pleased, happy, and gratified. A typical example is 愉快 yúkuài, meaning pleasant, but it is not at a point of happiness. The pleasant feeling might last longer for a certain time. In addition, it is quite low-key and not much of the expression is shown on the outside or physically. For example, 他们在中国的旅行十分愉快。Another example is 快乐 kuàilè meaning happy too but it is almost never used in conversation or oral expression. Instead, it is usually used for festival greetings. For example,
• 祝你生日快乐! Zhù nǐ shēngrì kuàilè! Happy birthday to you!
• 新年快乐！Xīnnián kuàilè! Happy New Year!
In addition, it means straightforward, forthright, and plainspoken. For example,
人们夸奖汤姆是个勇敢的小伙子，性格爽快，为人诚实。
rén men kuā jiǎng tāng mǔ shì gè yǒng gǎn de xiǎo huǒ zi , xìng gé shuǎng kuài , wéi rén chéng shí.
Tom was honoured with the appellations of a brave lad, a jolly dog, and an honest fellow.
（爽快 here means frank, straightforward, outright.)
当我请求他去机场接我时，他很爽快地答应了。
dāng wǒ qǐng qiú tā qù jī chǎng jiē wǒ shí , tā hěn shuǎng kuài de dā ying le 。
When I asked him to pick me up at the airport, he said yes without hesitation.
他请我同他痛痛快快地喝几杯。
tā qǐng wǒ tóng tā tòng tòng kuài kuài de hē jǐ bēi 。
He asked me to crack a bottle with him.
（痛快 here means very happy, delighted, joyful, and to one's heart's content or to one's great satisfaction.）
她没有迟疑，痛快地答复了。
tā méi yǒu chí yí , tòng kuài de dá fù le 。
She didn't hesitate for a moment but came straight out with her reply.
（痛快 here means simple and direct, forthright, and straightforward.）
练习: tell the meaning of 快 in the following sentences:
- 父亲看来没注意到我的不快，坐下来吃晚饭了。
- 他说得太快，她跟不上。
- 她说话爽快，总是坦白地说出她对别人的看法。
- 他说：“我玩得很痛快，那儿的人也很棒。”
- 匆匆回去，匆匆离开，离家快一年了，家那边变得怎样了？
