(bum) noun
1. U.S. Colloq. A worthless or dissolute loafer; tramp.
2. A spree; debauch.
—on the bum
1. Out of order; broken.
2. Living as a vagrant.
—adjective Bad; inferior.
—v. bum·med, bum·ming v.i.
1. To live by sponging from others.
2. To live idly and in dissipation.
—v.t.
3. To get by begging: to bum a ride. [Short for bummer, alter. of G bummler loafer, dawdler]
—bum′mer noun

(bum) v.i. bummed, bum·ming Brit. Dial.
To hum, as a top. [Var. of BOOM²]

(bum) noun Brit. Slang
The buttocks. [ME bom; origin uncertain]