ornythorhynchus, n. — Green’s Dictionary of Slang

ornythorhynchus n.

[SE ornithorhynchus, a duck-billed platypus, i.e. the punning ‘beast with a bill’]

(Aus.) a creditor.

1890		Dead Bird (Sydney) 26 Apr. 1/4: ‘Get out you ornithorhynchus!’ [...] ‘Who’s that?’ inquired a friend of the speaker. ‘An ornithorhynchus [...] Webster defines him as a beast with a bill’.
1890–1904		Farmer & Henley Sl. and Its Analogues.