Thrum n. [Written also thrumb.]
1. One of the ends of weaver's threads; hence, any soft, short threads or tufts resembling these.
2. Any coarse yarn; an unraveled strand of rope.
3. Bot. A threadlike part of a flower; a stamen.
4. Mining A shove out of place; a small displacement or fault along a seam.
5. Naut. A mat made of canvas and tufts of yarn.
Thrum cap, a knitted cap. --Halliwell.
Thrum hat, a hat made of coarse woolen cloth. --Minsheu.