Source : Webster's Revised Unabridged Dictionary (1913)

Verticillaster \Ver`ti*cil*las"ter\, a. [NL., fr. L. verticillus
   a whirl + aster a star.] (Bot.)
   A whorl of flowers apparently of one cluster, but composed of
   two opposite axillary cymes, as in mint. See Illust. of
   {Whorl}.