forcer

noun

1. (agent, form-of)Agent noun of force.
2. The solid piston of a force pump; the instrument by which water is forced in a pump.
3. A small hand pump for sinking pits, draining cellars, etc.
4. A bell-shaped lidded pot for growing rhubarb, used to limit photosynthesis by excluding light, encouraging early-season growth and blanched stems.