riser

noun

1. a person who rises, especially from bed: to be an early riser.
2. the vertical face of a stair step.
3. any of a group of long boards or narrow platforms that can be combined in stepwise fashion: The choir stood on a horseshoe of risers behind the orchestra.
4. a vertical pipe, duct, or conduit.
5. Metallurgy. a chamber or enlarged opening at the top of a mold for allowing air to escape or adding extra metal.
6. Nautical.
   1. a heavy strake of planking in the vicinity of the garboard strake in a wooden vessel.
   2. rising(def 10).

noun

1. a person who rises, esp from bedan early riser
2. the vertical part of a stair or step
3. a vertical pipe, esp one within a building