Billy

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mid 19th century: probably from Scots dialect billy-pot, possibly reinforced by bouilli tin or bully tin, an empty tin that had contained ‘bully beef’ (see bully3), used as a cooking utensil.

wiktionary

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billy (plural billies)

Of uncertain origin, but probably extracted from Scots billypot(“a type of cooking pot”).

etymonline

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billy (n.)

"club," 1848, American English, originally burglars' slang for "crowbar;" meaning "policeman's club" first recorded 1856, probably from nickname of William, applied to various objects (compare jack, jimmy, jenny). But compare French bille "a short, stout stick" (see billet (n.1)). Billy-goat as a familiar name for a male goat is from 1826.