Merriam-Webster's Collegiate® Dictionary, 11th Edition
BUM
I. noun
Etymology: Middle English bom
Date: 14th century
buttocks,
II. adjective
Etymology: perhaps from 4bum
Date: 1859
1. of poor quality or nature , not valid or deserved , not pleasant or enjoyable , affected or disabled by damage or injury ,
III. verb (bummed; bumming)
Etymology: probably back-formation from 1bummer
Date: 1863
intransitive verb loaf , to spend time unemployed and often wandering, transitive verb to obtain by asking or begging ; cadge ,
IV. noun
Etymology: probably short for 1bummer
Date: 1864
1. one who sponges off others and avoids work, one who performs a function poorly , one whose time is devoted to a recreational activity , vagrant , tramp ,
V. noun
Etymology: perhaps from 3bum
Date: 1863
a drinking spree ; bender , V
I. transitive verb
Etymology: probably back-formation from 2bummer
Date: 1973
disappoint , depress