Source : Webster's Revised Unabridged Dictionary (1913)

Quincuncial \Quin*cun"cial\, [L. quincuncialis, from quincunx.
   See {Quincunx}.]
   1. Having the form of a quincunx.

   2. (Bot.) Having the leaves of a pentamerous calyx or corolla
      so imbricated that two are exterior, two are interior, and
      the other has one edge exterior and one interior; as,
      quincuncial [ae]stivation.

   {Quincuncial phyllotaxy} (Bot.), an arrangement of five
      leaves in a spiral, each leaf two fifths of a circle from
      the next.