The Collaborative International Dictionary of English v.0.48:

Thrum \Thrum\ (thr[u^]m), n. [OE. thrum, throm; akin to OD.
   drom, D. dreum, G. trumm, lump, end, fragment, OHG. drum end,
   Icel. [thorn]r["o]mr edge, brim, and L. terminus a limit,
   term. Cf. Term.] [Written also thrumb.]
   1. One of the ends of weaver's threads; hence, any soft,
      short threads or tufts resembling these.
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   2. Any coarse yarn; an unraveled strand of rope.
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   3. (Bot.) A threadlike part of a flower; a stamen.
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   4. (Mining) A shove out of place; a small displacement or
      fault along a seam.
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   5. (Naut.) A mat made of canvas and tufts of yarn.
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   Thrum cap, a knitted cap. --Halliwell.

   Thrum hat, a hat made of coarse woolen cloth. --Minsheu.
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