Green’s Dictionary of Slang

blue moon n.

[rhy. sl.]

1. a spoon.

[UK]S.T. Kendall Up the Frog.
[UK]Partridge DSUE (8th edn) 103/1: late C.19–20.
[UK]B. Kirkpatrick Wicked Cockney Rhy. Sl.

2. (Aus.) a pimp.

[Aus]J. McNeil Chocolate Frog 48: An’ you call yourself a crim...pigs! The right name is egg-and-spoon, ain’t it, Shirk? Yer a terry-toon, a blue-moon...anythin’ that rhymes with weak-bludger-hoon!