Brass razoo is an Australian phrase that was first recorded in soldiers' slang in World War I. It is defined in the Oxford English Dictionary as "a non-existent coin of trivial value".^[1] It is commonly used in the expression I haven't got a brass razoo, meaning the speaker is out of money.

Whilst mock coins of 1 Razoo are occasionally produced, no actual monetary unit has ever been so named. Some speculate that the term arises from Egyptian or Indian currency.^{[citation needed]}

Etymologists and lexicographers have disputed and considered theories of the origins of the phrase, but most find no theory satisfactory.^[2]

Razoo may be a corruption of a sou, the smallest French coin.^{[citation needed]} Brass is a common slang term for 'money'.^[1]

Eric Partridge, in his Dictionary of Slang and Unconventional English, cites the Māori word rahu. Harry Orsman's Dictionary of New Zealand English (1997) makes a more confident conjecture.^[2]

As The Washington Post reported in December 2007, a Washington, D.C. firm established to facilitate social networking for philanthropy has taken its name from the New Zealand meaning of razoo for a small coin.^[3]

Another posited origin is a phrase used by Australian soldiers serving in France, and considered a joking reference used between Australian infantry and American troops. It was based on the Yankee "blowing a raspberry" also called a "razoo", a mouth-sound made to sound like a fart.^[2]

• Three-dollar bill