The Collaborative International Dictionary of English v.0.48:

Bum \Bum\ (b[u^]m), n. [Contr. fr. bottom in this sense.]
   The buttock. [Low] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   to bum around to wander about idly or aimlessly.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

bum \bum\ (b[u^]m), v. t.
   To borrow without intention of returning; to cadge; as, to
   bum a cigarette; to bum a cup of coffee; -- usually with
   inexpensive items as the object. [informal]
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Bum \Bum\, n.
   A humming noise. --Halliwell.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bum
    adj 1: of very poor quality; flimsy [syn: bum, cheap,
           cheesy, chintzy, crummy, punk, sleazy, tinny]
    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, bum, 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, bum]
    3: person who does no work; "a lazy bum" [syn: idler,
       loafer, do-nothing, layabout, bum]
    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, bum, 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]
    v 1: ask for and get free; be a parasite [syn: mooch, bum,
         cadge, grub, sponge]
    2: be lazy or idle; "Her son is just bumming around all day"
       [syn: bum, bum around, bum about, arse around, arse
       about, fuck off, loaf, frig around, waste one's
       time, lounge around, loll, loll around, lounge
       about]

Moby Thesaurus II by Grady Ward, 1.0:

223 Moby Thesaurus words for "bum":
   Arab, Bowery bum, amiss, arse, ass, backside, bad, barfy,
   bat around, beach bum, beachcomber, beg, beggar, beggarly fellow,
   bender, birr, blighter, bo, bombilate, bombinate, boom, booze,
   boozehound, bottle sucker, bottom, brannigan, budmash, bumble,
   bummer, burr, bust, butt, buzz, cadge, cadger, caitiff, can,
   carouse, cheeks, cheesy, count ties, crappy, creepy, crummy,
   derelict, derriere, devil, dirty, dissatisfactory, divagate,
   do-nothing, dogie, dolittle, drift, drifter, drone, drunk,
   drunkard, elbow bender, faineant, fanny, flit, floater, gad,
   gad about, gallivant, gamin, gamine, ginhound, go about,
   go the rounds, godawful, goldbrick, good-for-naught,
   good-for-nothing, goof off, goshawful, grim, guttersnipe, hairy,
   hind end, hit, hit the road, hit the trail, hit up, hobo,
   homeless waif, hooch hound, hum, human wreck, icky, idler, jag,
   jaunt, keister, knock about, knock around, landloper, laze, lazy,
   lazybones, lazzarone, loaf, loafer, loiter, loll, losel, lounge,
   lowlife, lush, lusher, mauvais sujet, mean wretch, meander,
   mendicant, mendicant friar, mendicant order, mooch, moocher,
   mucker, mudlark, no-good, nomadize, panhandle, panhandler,
   pass the hat, pauvre diable, peregrinate, pererrate, piker,
   pilgarlic, poor, poor creature, poor devil, posterior, prat, prowl,
   punk, purr, putrid, ragamuffin, ragman, ragpicker, ramble, range,
   roam, rotten, rounder, rove, rum hound, rummy, rump, run about,
   rusty-dusty, sad case, sad sack, saunter, schnorrer, scrounge,
   scrounger, shitty, ski bum, skid-row bum, slouch, slug, slugabed,
   soak, souse, sponge, stern, stew, stiff, stinking, stinky,
   straggle, stray, street Arab, street arab, street urchin, stroll,
   strum, sundowner, surf bum, swagman, swagsman, swillbelly,
   swillbowl, swillpot, tail, tatterdemalion, tennis bum, thrum,
   touch, traipse, tramp, truant, tuchis, turnpiker, tush, tushy,
   unsatisfactory, up, urchin, vag, vagabond, vagabondize, vagrant,
   vaurien, vomity, waif, waifs and strays, walk the tracks, wander,
   wassail, wastrel, wayfare, whir, whiz, wino, worthless fellow,
   wretch, wrong, yecchy



The Free On-line Dictionary of Computing (30 December 2018):

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]