The Collaborative International Dictionary of English v.0.48:

Snakeroot \Snake"root`\, n. (Bot.)
   Any one of several plants of different genera and species,
   most of which are (or were formerly) reputed to be
   efficacious as remedies for the bites of serpents; also, the
   roots of any of these.
   [1913 Webster]

   Note: The Virginia snakeroot is Aristolochia Serpentaria;
         black snakeroot is Sanicula, esp. Sanicula
         Marilandica, also Cimicifuga racemosa; Seneca
         snakeroot is Polygala Senega; button snakeroot is
         Liatris, also Eryngium; white snakeroot is
         Eupatorium ageratoides. The name is also applied to
         some others besides these.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cohosh \Co"hosh\, n. (Bot.)
   A perennial American herb (Caulophyllum thalictroides),
   whose rootstock is used in medicine; -- also called pappoose
   root. The name is sometimes also given to the Cimicifuga
   racemosa, and to two species of Act[ae]a, plants of the
   Crowfoot family.
   [1913 Webster] Cohune

WordNet (r) 3.0 (2006):

Cimicifuga racemosa
    n 1: North American bugbane found from Maine and Ontario to
         Wisconsin and south to Georgia [syn: black cohosh, black
         snakeroot, rattle-top, Cimicifuga racemosa]