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.

Source: Webster's Revised Unabridged Dictionary (1913)