Just to get you started!
The "A's":
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Abisselfa – By itself.
Abandons – Foundlings. Also applied to a street prostitute.
Above-Board – In open sight, without artifice, or trick.
Above One’s Bend – Out of one’s power, beyond reach.
Above Snakes – If you were “above snakes,” you were above ground – meaning still alive.
Absquatulate – To leave or disappear.
Ace in the Hole – A hideout or a hidden gun.
Ace-High – Depending upon the context, this might mean “first-class and respected”, or it could mean a winning poker hand.
According to Hoyle – Correct, by the book. “Hoyle” is a dictionary of rules for card playing games.
Acknowledge the Corn – To admit the truth, to confess a lie, or acknowledge an obvious personal shortcoming.
Acock – Knocked over, defeated, astounded, suddenly surprised.
Acorn Calf – A weak or runty calf.
Acquisitive – Booty, plunder.
Acreocracy – Signifies a landlord interest.
Across Lots – The fastest way possible, in the most expeditious manner.
Actual – Money.
Adam’s Ale – Water.
Addle-headed – Empty-headed, not smart.
Addle-pot – A spoilsport
Advantage – Pocket advantage – Carrying a derringer in a coat pocket that is charged and at half **** . Sometimes a shot is fired through the pocket itself.
Afeared – Scared, frightened.
Afterclaps – Unexpected happenings after an event is supposed to be over.
Afly – To become an expert at.
Agee, Ajee – Askew, crooked.
A Hog-Killin’ Time – A real good time. “We went to the Rodeo Dance and had us a hog-killin’ time.”
Airin’ the Lungs – A cowboy term for cussing.
Airin’ the Paunch – Vomit, throw-up, regurgitate. He’s “airing the paunch” after a heavy bout of drinking.
Airish – A little cool.
Air Line Road – A railroad track when it passes over the level unbroken prairie.
Airtights – Canned goods, such as canned beans, milk, or fruit.
Alfalfa Desperado – What cowboys often called a farmer.
A Lick and a Promise – To do a haphazard job. “She just gave it a lick and a promise.”
All Abroad – At a loss, not comprehending.
All Beer and Skittles – Unpleasant, not so happy.
All Down But Nine – Missed the point, not understood. This referenced missing all nine pins in bowling. (Yes, there was bowling during Old West times.)
All-fired – Very, great, immensely; used for emphasis. He is just too all-fired lazy to get any work done around here. Also “hell-fired” and “jo-fired.”
Allers – Always
All My Eye – Nonsense, untrue.
All Over – Bearing a resemblance to some particular object
All-overish – Uncomfortable. “I was just all-overish around that steely-eyed man.”
All the Caboose – Everywhere
All the Shoot – The whole assembly, all the party.
All to Pieces – Completely, absolutely.
Allot Upon – To intend, to form a purpose. “I allot upon going to Boston.”
All-Standing – Without preparation, suddenly.
Ambush – The scales used by grocers, coal-dealers, etc. Call such because the were always “lying in weight.”
Among the Willows – Dodging the Law.
Amputate Your Timber, or mahogany – Go way, run off.
Anasazi – Navajo for “ancient ones,” this word describes an ancient tribe of the Southwest. Some Navajo say this meaning is a mistranslation for a word that means “ancient enemies.” Another interpretation is “ancient ancestors.”
Angelicas – Young unmarried women.
Angolmaniacs – Another name for those “back east,” ultra-English.
Angoras – Hair-covered, goat-hide chaps. Especially good in cold weather.
Annex – To steal. This became popular at the time Texas was annexed, which was regarded by many as a theft.
Anti-fogmatic – Raw rum or whiskey. “I see that bartender is mixing a couple of anti-fogmatics.”
Anti-goglin – Lopsided.
Apple – Saddle horn.
Apple Jack – A liquor distilled from cider, also called cider brandy.
Apple Peeler – Pocket Knife
Apple Pie Order – In top shape, perfect order.
Making CoffeeArbuckle’s – Slang for coffee, taken from a popular brand of the time. “I need a cup of Arbuckle’s.”
Argufy – Argue, to have weight as an argument.
Argy – Argue
Arikara (also Arikaree) – This term is believed to mean “horns,” after this tribe’s ancient custom of wearing hair ornaments that stuck upright and were made of bone.
Arkansas Toothpick – A long, sharp knife. Also known as a California or Missouri toothpick.
Armas – Spanish forerunner of chaps. Cowboys fastened two large pieces of cowhide to the side of the saddle that protected their legs from thorns and brush.
Ary – Either.
Ash-Hopper – A lie cask, or box for ashes, resembling a hopper in a mill.
Ask No Adds – Ask no favor.
At Sea – At a loss, not comprehending. “When it comes to understanding women, I’m at sea.”
Attitudinize – To assume an affected attitude.
Atween – Between.
Atwixt – Between. “There were hard feelings atwixt them.”
Auger – The big boss.
Axle Grease – Butter
Tons more here!:
https://www.legendsofamerica.com/we-slang/[This message has been edited by Boondawg (edited 12-12-2019).]