Source : Webster's Revised Unabridged Dictionary (1913)

Slub \Slub\, n. [Etymol. uncertain.]
   A roll of wool slightly twisted; a rove; -- called also
   {slubbing}.

Slub \Slub\, v. t. [imp. & p. p. {Slubbed}; p. pr. & vb. n.
   {Slubbing}.]
   To draw out and twist slightly; -- said of slivers of wool.

Source : WordNet®

slub
     n : soft lump or unevenness in a yarn; either an imperfection or
         created by design [syn: {knot}, {burl}]