Source : Webster's Revised Unabridged Dictionary (1913)

Hydrorhiza \Hy`dro*rhi"za\, n.; pl. L. {Hydrorhiz[ae]}, E.
   {Hydrorhizas}. [NL., fr. E. hydra + Gr. ? a root.] (Zo["o]l.)
   The rootstock or decumbent stem by which a hydroid is
   attached to other objects. See Illust. under {Hydroidea}.