coin2 [transitive ]
to invent a new word or expression, especially one that many people start to use:
The word 'aromatherapy' was coined in the 1920s.
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 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.
to make pieces of money from metal