Source : Webster's Revised Unabridged Dictionary (1913)

Hydropiper \Hy"dro*pi`per\, n. [NL., fr. Gr. "y`dwr water + L.
   piper a pepper.] (Bot.)
   A species ({Polygonum Hydropiper}) of knotweed with acrid
   foliage; water pepper; smartweed.