The Collaborative International Dictionary of English v.0.48:

Thrum \Thrum\, v. t.
   1. To play, as a stringed instrument, in a rude or monotonous
      manner.
      [1913 Webster]

   2. Hence, to drum on; to strike in a monotonous manner; to
      thrum the table.
      [1913 Webster]

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.
      [1913 Webster]

   2. Any coarse yarn; an unraveled strand of rope.
      [1913 Webster]

   3. (Bot.) A threadlike part of a flower; a stamen.
      [1913 Webster]

   4. (Mining) A shove out of place; a small displacement or
      fault along a seam.
      [1913 Webster]

   5. (Naut.) A mat made of canvas and tufts of yarn.
      [1913 Webster]

   Thrum cap, a knitted cap. --Halliwell.

   Thrum hat, a hat made of coarse woolen cloth. --Minsheu.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thrum \Thrum\, v. t. [imp. & p. p. Thrummed; p. pr. & vb. n.
   Thrumming.]
   1. To furnish with thrums; to insert tufts in; to fringe.
      [1913 Webster]

            Are we born to thrum caps or pick straw? --Quarles.
      [1913 Webster]

   2. (Naut.) To insert short pieces of rope-yarn or spun yarn
      in; as, to thrum a piece of canvas, or a mat, thus making
      a rough or tufted surface. --Totten.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thrum \Thrum\, v. i. [CF. Icel. ?ruma to rattle, to thunder, and
   E. drum.]
   1. To play rudely or monotonously on a stringed instrument
      with the fingers; to strum.
      [1913 Webster]

   2. Hence, to make a monotonous drumming noise; as, to thrum
      on a table.
      [1913 Webster]

WordNet (r) 3.0 (2006):

thrum
    n 1: a thrumming sound; "he could hear the thrum of a banjo"
    v 1: sound with a monotonous hum [syn: hum, thrum]
    2: sound the strings of (a string instrument); "strum a guitar"
       [syn: strum, thrum]
    3: make a rhythmic sound; "Rain drummed against the windshield";
       "The drums beat all night" [syn: drum, beat, thrum]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "thrum":
   barrage, beat, beat a ruffle, beat a tattoo, beat the drum,
   beat time, beating, birr, bombilate, bombinate, boom, bum, bumble,
   burr, buzz, count, count the beats, drone, drum, drum music,
   drumbeat, drumfire, drumming, flutter, go pitapat, hum, keep time,
   palpitate, palpitation, paradiddle, patter, pick, pitapat,
   pitter-patter, play drum, pluck, plunk, pound, pounding, pulsate,
   pulsation, purr, rat-a-tat, rat-tat, rat-tat-tat, rataplan,
   rattattoo, roll, rub-a-dub, ruff, ruffle, sound a tattoo, spatter,
   splatter, splutter, sputter, staccato, strum, sweep the strings,
   tap, tat-tat, tattoo, throb, throbbing, thump, thumping, tom-tom,
   twang, whir, whiz