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”. 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 popular no actual monetary unit has ever been so named. Some speculate that the term arises from Egyptian or Indian currency. In one fictional dialogue, the razoo has been described as “an Indian coin, famous for being the most worthless coin ever issued.”
Etymologists and lexicographers have disputed and considered theories of the origins of the phrase, but most find no theory satisfactory.
*Some additional information taken from Wikipedia for education purposes only.