The Collaborative International Dictionary of English v.0.48:

Crumb \Crumb\ (kr[u^]m), n. [AS. cruma, akin to D. kruim, G.
   krume; cf. G. krauen to scratch, claw.] [Written also
   crum.]
   1. A small fragment or piece; especially, a small piece of
      bread or other food, broken or cut off.
      [1913 Webster]

            Desiring to be fed with the crumbs which fell from
            the rich man's table.                 --Luke xvi.
                                                  21.
      [1913 Webster]

   2. Fig.: A little; a bit; as, a crumb of comfort.
      [1913 Webster]

   3. The soft part of bread.
      [1913 Webster]

            Dust unto dust, what must be, must;
            If you can't get crumb, you'd best eat crust. --Old
                                                  Song.
      [1913 Webster]

   Crumb brush, a brush for sweeping crumbs from a table.

   To a crum, with great exactness; completely.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Crumb \Crumb\, v. t. [imp. & p. p. Crumbed (kr[u^]md); p. pr.
   & vb. n. Crumbing (kr[u^]m"[i^]ng).]
   To break into crumbs or small pieces with the fingers; as, to
   crumb bread. [Written also crum.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

crumb
    n 1: a very small quantity of something; "he gave only a crumb
         of information about his plans"; "there were few crumbs of
         comfort in the report"
    2: 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]
    3: small piece of e.g. bread or cake
    v 1: coat with bread crumbs; "crumb a cutlet"
    2: break into crumbs
    3: remove crumbs from; "crumb the table"

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "crumb":
   abrade, air pollution, atom, atomize, attritus, beat, besprinkle,
   bit, bite, bran, bray, bread, brecciate, butt, chip, chunk, clip,
   clipping, collop, comminute, contriturate, cosmic dust, crumble,
   crush, cut, cutting, disintegrate, dollop, dot, dram, dredge, drop,
   droplet, dust, dust ball, efflorescence, end, fallout, farina,
   filings, fleck, flour, flyspeck, fragment, gnat, gob, gobbet,
   grain, granulate, granulize, grate, grind, grind to powder, grits,
   groats, hunk, iota, jot, kittens, levigate, lint, lota, lump, mash,
   meal, microbe, microorganism, midge, mill, minim, minutia,
   minutiae, mite, modicum, moiety, molecule, morceau, morsel, mote,
   nip, ounce, paring, particle, patch, pepper, pestle, piece,
   pinhead, pinpoint, point, pound, powder, pulverize, pussies,
   rasher, raspings, reduce to powder, sawdust, scintilla, scoop,
   scrap, scrunch, shard, shaving, shiver, shred, slice, sliver,
   smash, smidgen, smithereen, smut, snack, snatch, snick, snip,
   snippet, soot, spatter, speck, speckle, splatter, splinter, spot,
   sprinkle, squash, stitch, stud, stump, tag, tatter, tittle,
   triturate, vanishing point



The Jargon File (version 4.4.7, 29 Dec 2003):

crumb
 n.

    Two binary digits; a quad. Larger than a bit, smaller than a nybble.
    Considered silly. Syn. tayste. General discussion of such terms is under
    nybble.


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

crumb
quarter
tayste

    (Or tayste /tayst/) Silly suggested term for
   two binary digits.

   The term "quarter" has also been suggested, referring to the
   US 25-cent coin.  This was once equal in value to two of the
   eight "bits" - pie-slice-shaped "pieces of eight" - into which
   Spanish silver crowns were cut to make change.

   [Jargon File]

   (2007-05-31)