The Collaborative International Dictionary of English v.0.48:

Arhizal \A*rhi"zal\, Arhizous \A*rhi"zous\, Arhythmic
\A*rhyth"mic\, Arhythmous \A*rhyth"mous\, a.
   See Arrhizal, Arrhizous, Arrhythmic, Arrhythmous.
   [1913 Webster]