B
| "Bark Juice" | Liquor or strong adult beverage |
| "Barrel Shirt" | Barrel worn by thieves for punishment |
| "Beehive" | Knapsack |
| "Been through the mill" | Bad day |
| "Blowhard" | A big shot or braggart |
| "Blue Jacket" | Union sailor |
| "Blue Mass" | Refers to men on sick call; named after blue pill |
| "Bluff" | Cheater |
| "Bombproofs" | A shelter from artillery attacks |
| "Bounty" | Monetary sum of money for enlistment in the Army |
| "Bragg's Body Guard" | Body lice |
| "Bread bag" | Haversack |
| "Bread basket" | Stomach |
| "Brevet" | Awarded higher rank due to meritous service in combat |
| "Bugger" | Officer |
| "Bull Pit" | Under-arrest confinement area |
| "Bully" | Yeah or Hurrah! |
| "Bumblebee" | Sound of flying miniballs |
| "Bummer" | A loafer or forager |
| "Bummer's Cap" | Regulation fatigue or forage cap |
| "Bust Head" | Home-brewed or camp-brewed beer |
| "Buttermilk Cavalry" | Term infantry had for cavalry |
| "Butternuts" | Yellowish-brown dyed uniforms made of copperas and walnut hulls, when grey coloring was in short stock |