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.