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.
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            Desiring to be fed with the crumbs which fell from
            the rich man's table.                 --Luke xvi.
                                                  21.
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   2. Fig.: A little; a bit; as, a crumb of comfort.
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   3. The soft part of bread.
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            Dust unto dust, what must be, must;
            If you can't get crumb, you'd best eat crust. --Old
                                                  Song.
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   Crumb brush, a brush for sweeping crumbs from a table.

   To a crum, with great exactness; completely.
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