[bum] n [ME bom] (14c) chiefly Brit: buttocks--sometimes considered vulgar
[2]bum adj [perh. fr. [4]bum] (1859) 1 a: of poor quality or nature: invalid, inferior "~ advice" "a ~ check" b: acutely disagreeable "a ~ trip"
2: not functioning because of damage or injury: disabled "a ~ knee" [3]bum vb bummed ; bum.ming [prob. back-formation fr. [1]bummer] vi (1863) 1: loaf
2: to spend time unemployed and often wandering--often used with around ~ vt: to obtain by begging: cadge [4]bum n [prob. short for bummer] (1864) 1 a: one who sponges off others and avoids work b: one who performs a function poorly "called the umpire a ~" c: one who devotes his time to a recreational activity "a beach ~" "ski ~s"
2: vagrant, tramp -- on the bum : with no settled residence or means of support [5]bum n [prob. fr. [3]bum] (1871): a drinking spree: bender