noun a worthless horse.
2. plug ·noun a high, tapering silk hat.
3. plug ·noun a flat oblong cake of pressed tobacco.
4. plug ·vt to stop with a plug; to make tight by stopping a hole.
5. plug ·noun a block of wood let into a wall, to afford a hold for nails.
6. plug ·noun any piece of wood, metal, or other substance used to stop or fill a hole; a stopple.