The Collaborative International Dictionary of English v.0.48:

Tarragon \Tar"ra*gon\, n. [Sp. taragona, Ar. tarkh?n; perhaps
   fr. Gr. ? a dragon, or L. draco; cf. L. dracunculus tarragon.
   Cf. Dragon.] (Bot.)
   A plant of the genus Artemisa (Artemisa dracunculus),
   much used in France for flavoring vinegar.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tarragon
    n 1: aromatic perennial of southeastern Russia [syn: tarragon,
         estragon, Artemisia dracunculus]
    2: fresh leaves (or leaves preserved in vinegar) used as
       seasoning [syn: tarragon, estragon]