Of obscure origin. Perhaps a variant of bully (“companion, mate, comrade”). Compare Scots billie (“a comrade; companion”). Compare also Middle Low German billig (“equitable, reasonable, lawful, fitting, according to natural law, just”).
Meanings
A fellow, companion, comrade, mate; partner, brother.
(Geordie) A good friend.
Fareweel, my rhyme-compoſing billie! / Your native ſoil was right ill-willie; / But may ye flouriſh like a lily, / Now bonilie! / I'll toaſt ye in my hindmoſt gillie, / Tho' owre the Sea! 1786 July 31, Robert Burns, “On a Scotch Bard Gone to the West Indies”, in Poems, Chiefly in the Scottish Dialect, Kilmarnock, East Ayrshire: Printed by John Wilson, →OCLC; reprinted Kilmarnock: James McKie, March 1867, →OCLC, page 184:
A billy goat.
1970 August, Valerius Geist, Mountain Goat Mysteries, Field & Stream, page 62,
Then, during three days, I was amazed to see nannies with kids attack and chase off large billies.
It isn't just billies that enter the bleak season with rut-depleted fat reserves, but rams, bull elk, buck deer, and others. 2002, Douglas H. Chadwick, A Beast the Color of Winter: The Mountain Goat Observed, page 159:
In fact, distinguishing between billies and nannies isn't necessarily a sure thing. 1992, Dwight R. Schuh, “Mountain Goat (Oreamnos americanus)”, in Bowhunter's Encyclopedia, page 276:
(UK, obsolete, slang) A silk handkerchief.
All fighting coves you too must know, / Ben Caunt as well as Bendigo, / And to each mill be sure to go, / […] And you must sport a blue billy, / Or a yellow wipe […] 1859, Ducange Anglicus, The Vulgar Tongue, page 54:
Uncertain, but probably extracted from Scots billypot (“a type of cooking pot”), perhaps originally from the name Billy, a diminutive of William.
The condom sense from the E-Rotic song Willy, Use a Billy... Boy, referring in turn to Billy Boy, a German brand of condoms.
Meanings
A highwayman's club, billy club.
A slubbing or roving machine.
[…]at the time there existed in Dublin and its immediate neighbourhood, “forty-five manufacturers, having twenty-two billies, giving employment to 2885 work people, on whom depended for support 7386 individuals, manufacturing 29,312 pieces of cloth, of various qualities, valued at £336,380.” 1840, The Citizen, page 347:
On the second floor there were 2 billies, 1 carding and 1 scribbling machine. 1967, Jennifer Tann, Gloucestershire Woollen Mills: Industrial Archaeology, page 126:
(Australia, New-Zealand) A tin with a swing handle used to boil tea over an open fire; a billycan; a billypot.
Let's get the billy and cook some beans.
By the fire the billies were boiling, the tucker of both camps spread out on tarpaulins. 1937, Ion L. Idriess, Over the Range, Sydney: Angus and Robertson, published 1947, page 10:
We had been absent from civilisation, so long, that our tin billies, the only boiling utensils we had, got completely worn or burnt out at the bottoms, and as the boilings for glue and oil must still go on, what were we to do with billies with no bottoms? 1889, Ernest Giles, Australia Twice Traversed, published 2004, page 239:
Mother prepared a splendid picnic. […] Rugs, food and the black billy for making tea, were packed into the old baby buggy and we trundled it straight down Simcoe Street. 1942, Emily Carr, “Loyalty”, in The Book of Small, Toronto, Ont.: Oxford University Press, →OCLC:
Oh there once was a swagman camped in the billabong,
Under the shade of a coolibah tree,
And he sang as he looked at the old billy boiling,
'Who'll come a'waltzing Matilda, with me.' 1895, “Waltzing Matilda”, Banjo Paterson (lyrics):
Over the fence, in a shallow gully 100 metres away, this guy and his wife were living on the dirt in the open weather with just a blanket, billies, a dog and a transistor radio. They didn't even have water. 2011, Rod Moss, The Hard Light of Day: An Artist's Story of Friendships in Arrernte Country, unnumbered page: