In a triangle with a right angle (one corner of 90 degrees), the sine of one of the other angles is a fraction: take the side opposite that angle and divide it by the longest side — the side opposite the right angle, called the hypotenuse. People write it sin, so sin 30° = 1/2.

In a triangle with a right angle在一個有直角的三角形裡 (one corner of 90 degrees)（一個角是90度），the sine of one of the other angles其中一個角的sine is是 a fraction一個分數：take the side opposite that angle拿那個角對面的邊 and divide it by the longest side除以最長的那邊——the side opposite the right angle也就是直角對面的那邊，called the hypotenuse叫做斜邊。People write it sin人們會寫成sin，so sin 30° = 1/2所以sin 30° = 1/2。

You meet it in school trigonometry, and later in science: a sine wave is the smooth up-and-down curve this function draws.

You meet it你會遇到它 in school trigonometry在學校的三角函數課裡，and later也會在 in science後來的科學裡：a sine wave正弦波（sine wave） is就是 the smooth up-and-down curve那種平滑上下起伏的曲線 this function draws這個函數畫出來的。

Though actually, the English word has a messy birth. Latin sinus meant a curve, a fold, a bosom. Medieval scholars used it to translate an Arabic maths word. The Arabic letters were written without vowels and looked like the word for “bosom,” but they stood for a different Arabic word meaning sine, which had come from a Sanskrit word for a bowstring (a chord of a circle looks like a string on a bow). So sine is something of a translation accident, and it is a doublet of sinus — same Latin parent, different life in English.

Though actually不過其實，the English word這個英文字 has a messy birth身世有點亂。Latin sinus拉丁文sinus meant原本指的是 a curve, a fold, a bosom彎曲、摺痕，或是胸部。Medieval scholars中世紀的學者 used it曾用它 to translate an Arabic maths word來翻譯一個阿拉伯文的數學詞。The Arabic letters阿拉伯文的字母 were written without vowels原本不寫母音 and looked like the word for "bosom,"看起來像是「胸部」那個詞，but they但它們其實 stood for a different Arabic word代表的是另一個阿拉伯字 meaning sine意思是sine，which had come from a Sanskrit word for a bowstring而那個字是從一個意思是弓弦的梵文字來的 (a chord of a circle looks like a string on a bow)（因為圓的弦看起來就像弓上的一條弦）。So所以 sine is something of a translation accidentsine某種程度上算是翻譯上的意外，and it is a doublet of sinus它和sinus是一對doublet（同源雙生詞）——same Latin parent, different life in English出自同一個拉丁文祖先，卻在英文裡走上了不同的路。

The job-word sinecure uses a different Latin sine, meaning “without.” That is not this word.

The job-word sinecure表示工作的那個字sinecure uses用的是 a different Latin sine另一個拉丁文sine, meaning "without."意思是「沒有」。That那 is not this word跟這個字不是同一個。