A random anecdotal story about the definition of money:
My dad was a banker. Before that though, he went to Columbia University to get a degree in banking (10 years of night school in the fifties and sixties, he was still going when I was a kid).
He was in a semester-long Money and Banking class that had homework and other tests but for which the vast majority of the grade was determined by the results of the final exam. (what follows only makes sense if you realize that my dad could be a very stubborn Old World curmudgeon)
He went into the exam room expecting pages and pages of questions about M1, fractional reserves, the velocity of money, bank regulations, interest rates, etc. Instead, the professor wrote three words on the chalkboard: What is money?
Other students started writing (presumably about M1, fractional reserves, the velocity of money, bank regulations, interest rates, etc.) but my dad sat there steaming. Finally couldn't take it any more. He took out a pencil, wrote Money is sweat. , handed his test sheet to the professor, and walked out the door.
He got an F for the class, had to re-take it next semester. Gave the answers that were expected, and got an A the next time.
But he was basically right the first time.