在很多情况下，这两个词是这可以互换使用的，也就是说，这两个词的意思非常相近。一般而言，till 用于肯定句，untill 用于否定句。但是，这两个词在意义上也是有细微差别的。
英美国家的英语语法教师是这样来描述这两个字的分别的：
“Till” is used to mean the time up to a particular instance and the action can continue even after that.
“Until” is used to mean the time up to a particular instance and the speaker has in mind that the action after this time does not almost happen.
翻译成中文来理解就是：
Till是指直到某一特定事件发生的时候，而在那个时刻之后，该事情或状况仍将持续。
Until是指直到某一特定事件发生的时候，而讲话的人在自己心里认为，在那个时刻之后，该事情或该状况将中止（不怎么可能持续）。
这应该把一切都说得很明白了。
一、Till 用法示例：
1. People do not know the value of health till they lose it.
直到失去健康，人们才知道健康的可贵。
2. I'll wait till four o'clock.
我将等到四点钟。
3. We must stick to our task till it is finished.
我们必须继续工作, 直至做好为止。
4. Not till then did I realize the danger of the situation.
直到那个时候我才感到形势的危险。
5. Never put off till tomorrow what you can do today.
今日事今日毕。
6. The people next door play their radio from morning till night.
邻居从早到晚开着收音机。
7. The meeting adjourned till five o'clock.
会议延至五点召开。
8. Gee, I can hardly wait till it's dark.
哎呀，我简直等不到天黑了。
二、Until 用法示例
1. I didn't wake up until I heard the alarm clock.
直到听到闹钟的铃声我才醒来。
2. He lived in California until he was twenty.
他在加里弗尼亚一直住到20岁.
3. She was a bank clerk until the war, when she trained as a nurse.
她战前是个银行职员，战时受训当了护士。
4. Wait until the rain stops.
等到雨停了再说吧.
5. Continue in this direction until you see a sign.
一直朝著这个方向走就看见指示牌了.
6. The secret was never told until after the old man's death.
这个秘密在老人去世后才说出来.
7. I won't stop shouting until you let me go.
你不放我走我就一直喊叫.
8. Until she spoke I hadn't realized she was foreign.
她要不说话我还一直不知道她是外国人.