The Collaborative International Dictionary of English v.0.48:

Amianthus \Am`i*an"thus\, n. [L. amiantus, Gr. ? ? (lit.,
   unsoiled stone) a greenish stone, like asbestus; 'a priv. + ?
   to stain, to defile; so called from its incombustibility.]
   (Min.)
   Earth flax, or mountain flax; a soft silky variety of
   asbestus.
   [1913 Webster]