Source : Webster's Revised Unabridged Dictionary (1913)

Bum \Bum\, n. [Contr. fr. bottom in this sense.]
   The buttock. [Low] --Shak.

Bum \Bum\, v. i. [imp. & p. p. {Bummed}; p. pr. & vb.n.
   {Bumming} (?).] [See {Boom}, v. i., to roar.]
   To make murmuring or humming sound. --Jamieson.

Bum \Bum\, n.
   A humming noise. --Halliwell.

Source : WordNet®

bum
     n 1: a person who is deemed to be despicable or contemptible;
          "only a rotter would do that"; "kill the rat"; "throw
          the bum out"; "you cowardly little pukes!"; "the British
          call a contemptible person a `git'" [syn: {rotter}, {dirty
          dog}, {rat}, {skunk}, {stinker}, {stinkpot}, {puke}, {crumb},
           {lowlife}, {scum bag}, {so-and-so}, {git}]
     2: a disreputable vagrant; "a homeless tramp"; "he tried to
        help the really down-and-out bums" [syn: {tramp}, {hobo}]
     3: person who does no work; "a lazy bum" [syn: {idler}, {loafer},
         {do-nothing}, {layabout}]
     4: the fleshy part of the human body that you sit on; "he
        deserves a good kick in the butt"; "are you going to sit
        on your fanny and do nothing?" [syn: {buttocks}, {nates},
        {arse}, {butt}, {backside}, {buns}, {can}, {fundament}, {hindquarters},
         {hind end}, {keister}, {posterior}, {prat}, {rear}, {rear
        end}, {rump}, {stern}, {seat}, {tail}, {tail end}, {tooshie},
         {tush}, {bottom}, {behind}, {derriere}, {fanny}, {ass}]
     [also: {bumming}, {bummed}]

bum
     v 1: ask for and get free; be a parasite [syn: {mooch}, {cadge},
          {grub}, {sponge}]
     2: be lazy or idle; "Her son is just bumming around all day"
        [syn: {bum around}, {bum about}, {arse around}, {arse
        about}, {fuck off}, {loaf}, {frig around}, {waste one's
        time}, {lounge around}, {loll}, {loll around}, {lounge
        about}]
     [also: {bumming}, {bummed}]

bum
     adj : of very poor quality [syn: {cheap}, {cheesy}, {chintzy}, {crummy},
            {punk}, {sleazy}, {tinny}]
     [also: {bumming}, {bummed}]

Source : Free On-Line Dictionary of Computing

bum
     
        1. To make highly efficient, either in time or space, often at
        the expense of clarity.  "I managed to bum three more
        instructions out of that code."  "I spent half the night
        bumming the interrupt code."  In {elder days}, {John McCarthy}
        (inventor of {Lisp}) used to compare some efficiency-obsessed
        hackers among his students to "ski bums"; thus, optimisation
        became "program bumming", and eventually just "bumming".
     
        2. To squeeze out excess; to remove something in order to
        improve whatever it was removed from (without changing
        function; this distinguishes the process from a
        {featurectomy}).
     
        3.  A small change to an algorithm, program, or hardware
        device to make it more efficient.  "This hardware bum makes
        the jump instruction faster."
     
        Usage: now uncommon, largely superseded by v. {tune} (and
        {tweak}, {hack}), though none of these exactly capture sense
        2.  All these uses are rare in Commonwealth hackish, because
        in the parent dialects of English "bum" is a rude synonym for
        "buttocks".
     
        [{Jargon File}]