Source : Webster's Revised Unabridged Dictionary (1913)

Sinistrorsal \Sin`is*tror"sal\, a. [L. sinistrorsus,
   sinistroversus, turned toward the left side; sinister left +
   vertere, vortere, versum, vorsum, to turn.]
   Rising spirally from right to left (of the spectator);
   sinistrorse.

Source : WordNet®

sinistrorsal
     adj : spiraling upward from right to left; "sinistrorse vines"
           [syn: {sinistrorse}]