pentachenium

from The Collaborative International Dictionary of English v.0.48

Pentachenium \Pen`ta*che"ni*um\, n. [NL. See {Penta-}, and
   {Achenium}.] (Bot.)
   A dry fruit composed of five carpels, which are covered by an
   epigynous calyx and separate at maturity.
   [1913 Webster]