billion n. [BILL-yun]
十亿
Definition
1 US: a number equal to 1,000 million; also, British: a number equal to 1,000 milliard
1: 【美】十亿；【英】milliard是十亿，billion是1,000个十亿，即一万亿。
2: a very large number.
2：一个非常非常大的数
注：在美国，billion是十亿，trillion是一万亿；在英国，milliard是十亿，billion是一万亿。
Did You Know?
How much is a billion? It might depend on whom you ask. Billion was borrowed from French in the late 1600s to indicate the number one million raised to the power of two, or a million million - a number represented by a 1 followed by 12 zeros. However, the French later changed their naming conventions so that a billion became a thousand million (a 1 followed by 9 zeros) and a trillion became a thousand thousand million (or a million million, the old billion). The French have since returned to the older system, but it was this new system that was adopted by American English speakers in the 1800s. In Britain, the newer system has seen increasing use since the 1950s, but the older sense is still sometimes used there as well.
词源词根演化：billion（French）--> Billion (English)
一个billion到底是多少？答案主要看你问的是什么人。billion这个单词是17世纪晚期从法语借来的，用于表示一百万的二次方，即一百万个一百万，即1后面跟着12个零（1,000,000,000,000），中文的一万亿。这是法语旧计数法。法国人后来更改了他们计数法。在新计数法中，让billion表示一千个一百万，即1后面跟着9个零（1,000,000,000），中文的十亿；用trillion表示一千个十亿billion，即中文一万亿，也即旧计数法的billion。现在法国人又回到了旧计数法，但是新计数法在19世纪被美国英语世界采纳并沿用至今。在英国，自1950年代，新计数法的使用也在逐渐的增加，但是旧计数法的含义有时候也还在使用。
Examples
- If you were to count to a billion at the rate of one number per second, it would take you over 31 and a half years to finish.
如果用每秒钟一个数字的速度数到十亿，大约需要花费31年半的时间。
注：1,000,000,000 / 60 / 60 / 24 / 365 = 31.71年，这里billion指的是十亿。
- "White dwarf stars start off extremely hot, but they no longer generate their own energy. And while they intially radiate enough heat that we can see them in out telescope, they slowly lose their energy over billions of years."
--- Deborah Netburn, The Bismark (North Dakota) Tribune, 15 Jan. 2019
白矮星开始变得极度炙热，但是它们已经不再产生能量。不过由于最初它们已经放射出了足够的热能，因此我们能从望远镜中观察到它们，在随后的亿万年里白矮星会逐渐的失去所有的能量。
注：这里的billion是虚指，并非精确的计数。