Source : Webster's Revised Unabridged Dictionary (1913)

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