forms of money and methods of payment

1. [countable] a piece of metal, usually flat and round, that is used as money ⇨ bill, note
2. 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:
Toss a coin to see who goes first.
3. the other/opposite side of the coin a different or opposite way of thinking about something:
Making the rules is only part of it. How the rules are carried out is the other side of the coin.
4. 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:
Great opportunity and great danger are two sides of the same coin.
5. [uncountable] money in the form of metal coins
• • •
THESAURUS
▪ money what you use to buy things, in the form of notes or coins: He spent all his money on computer equipment.
▪ cash money in the form of coins and notes: I didn’t have any cash with me.
▪ currency the money used in a particular country: The dollar gained in value against other currencies. | a single European currency
▪ change money in the form of coins of low value: Do you have any small change? | a pocketful of loose change
▪ note British English, bill American English a piece of paper money: a £20 note | a $5 bill
▪ coin a flat round piece of metal used as money: She put some coins in the parking meter. | He took a coin out of his pocket.
▪ a ten-pence/50-cent etc piece a coin worth a particular amount
II. coin² BrE AmE verb [transitive]
1. to invent a new word or expression, especially one that many people start to use:
The word ‘aromatherapy’ was coined in the 1920s.
2. 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:
He’d thought the flight would never – to coin a phrase – get off the ground.
3. coin money/coin it (in) British English informal to earn a lot of money very quickly:
BT at its profitable peak was coining it at the rate of £90 a second.
4. to make pieces of money from metal

Oxford Advanced Learner's Dictionary

coin

coin [coin coins coined coining] noun, verb [kɔɪn] [kɔɪn]

noun

1. countable a small flat piece of metal used as money

• a euro coin

2. uncountable money made of metal
• notes and coin
see the other side of the coin at side _n., two sides of the same coin at two
Word Origin:
Middle English: from Old French coin ‘wedge, corner, die’, coigner ‘to mint’, from Latin cuneus ‘wedge’. The original sense was ‘cornerstone’, later ‘angle or wedge’ (senses now spelled quoin); in late Middle English the term denoted a die for stamping money, or a piece of money produced by such a die.
Example Bank:
• The first English gold coin was struck in 1255.
• The last silver coins were minted in 1964.
• They flipped/tossed a coin to see who should go first.
• Very few old 5p coins are still in circulation.
• What is the probability of the coin landing heads?
• coins jingling in his pockets

Idioms: coin a phrase ▪ coining it ▪ coining money

verb
1. ~ sth to invent a new word or phrase that other people then begin to use

• The term ‘cardboard city’ was coined to describe communities of homeless people living in cardboard boxes.

2. ~ sth to make coins out of metal
Verb forms:

Word Origin:
Middle English: from Old French coin ‘wedge, corner, die’, coigner ‘to mint’, from Latin cuneus ‘wedge’. The original sense was ‘cornerstone’, later ‘angle or wedge’ (senses now spelled quoin); in late Middle English the term denoted a die for stamping money, or a piece of money produced by such a die.
Example Bank:

• He was the first to coin the motto ‘Make Love, Not War’.

Cambridge Advanced Learner's Dictionary

coin (MONEY) /kɔɪn/
noun
1 [C] a small round piece of metal, usually silver or copper coloured, which is used as money:
a 10p/ten pence coin
a pound coin
a ten-cent coin
gold coins
I asked for ten pounds in 20p coins.
That machine doesn't take 50p coins.

2 [U] money in the form of metal coins

Collins COBUILD Advanced Learner’s English Dictionary

coin

[kɔ͟ɪn]
coins, coining, coined
1) N-COUNT A coin is a small piece of metal which is used as money.
  ...50 pence coins.
  ...Frederick's gold coin collection.
2) VERB If you coin a word or a phrase, you are the first person to say it.
  [V n] Jaron Lanier coined the term `virtual reality' and pioneered its early development...
  [V n] The word `lunatic' was coined to describe people who went mad at the full moon.
3) VERB: usu cont (emphasis) If you say that someone is coining it or is coining money, you are emphasizing that they are making a lot of money very quickly, often without really earning it. [INFORMAL]
  [V it] Many private colleges are coining it...
  [V n] One wine shop is coining money selling Wembley-label champagne.
PHRASAL VERB
Coining in means the same as coining. V it P She's coining it in with a $10 million contract with Revlon.
4) PHRASE You say `to coin a phrase' to show that you realize you are making a pun or using a cliché.
  Fifty local musicians have, to coin a phrase, banded together to form the Jazz Umbrella.
5) PHRASE: PHR with cl You use the other side of the coin to mention a different aspect of a situation.
  These findings are a reminder that poverty pay is the other side of the coin of falling unemployment.
6) PHRASE: usu v-link PHR If you say that two things are two sides of the same coin, you mean that they are different ways of looking at or dealing with the same situation.
  The minister reportedly stressed that economic and political reforms were two sides of the same coin.

Merriam-Webster's Advanced Learner's Dictionary

Merriam-Webster's Advanced Learner's Dictionary:

¹coin /ˈkoɪn/ noun, pl coins [count] : a small, flat, and usually round piece of metal issued by a government as money
• gold/silver/copper coins
• I have a dollar in coins.
the other/opposite/flip side of the coin : a different way of looking at or thinking about a situation
• The economy is improving, but the other side of the coin is that inflation is becoming a bigger problem.
toss/flip a coin : to decide something by throwing a coin up in the air and seeing which side is shown after it lands
• Let's toss a coin. Heads, we don't go; tails, we do.
two sides of the same coin : two things that are regarded as two parts of the same thing
• These problems may seem unrelated but they are really two sides of the same coin.