The Collaborative International Dictionary of English v.0.48:

Priapean \Pri`a*pe"an\, n. [Cf. L. Priapeius pertaining to
   Priapus.] (Lat. Pros.)
   A species of hexameter verse so constructed as to be
   divisible into two portions of three feet each, having
   generally a trochee in the first and the fourth foot, and an
   amphimacer in the third; -- applied also to a regular
   hexameter verse when so constructed as to be divisible into
   two portions of three feet each. --Andrews.
   [1913 Webster]