[C] a piece of metal, usually flat and round, that is used as money

硬币;

toss / flip a coin, to choose or decide something by throwing a coin into the air and guessing which side of it will show when it falls

抛硬币作选择（决定）:

Toss a coin to see who goes first.

抛硬币来决定谁先来。

the other / opposite side of the coin, a different or opposite way of thinking about something

事情的另一面:

Making the rules is only part of it. How the rules are carried out is the other side of the coin.

制定出规定仅仅是事情的一方面，这些规定怎么执行则是另一回事了。

two sides of the same coin, two problems or situations that are so closely connected that they are really just two parts of the same thing

同一事情密切相关的两个方面:

Great opportunity and great danger are two sides of the same coin.

好机会和高风险是密切相关的。

[U] money in the form of metal coins

硬币，钱币

to invent a new word or expression, especially one that many people start to use

创造，杜撰〔新词等〕:

The word 'aromatherapy' was coined in the 1920s.

aromatherapy （芳香疗法）这个词是 20 世纪 20 年代创造出来的。

to coin a phrase, [spoken] said in a joking way when you use a very common expression, to show that you know it is used a lot

套句老话说，常言说得好:

He'd thought the flight would never – to coin a phrase – get off the ground.

他以为这趟航班是永远也不会 — 套句老话说 — 离地起飞了。

coin money / coin it (in), [BrE informal] to earn a lot of money very quickly

大发其财，暴富:

BT at its profitable peak was coining it at the rate of ￡90 a second.

英国电信公司在盈利高峰时以每秒 90 英镑的速度在赚钱。

to make pieces of money from metal

铸〔币〕