plumptitude

noun2

1. •
   (humorous) The quality or state of being plump.

   • His own sister is happy to oblige his fondness for rich fare and both are cushion-rump'd, with Mr. Butterwerthe's posterior greatly resembling that of his own sister's in its plumptitude. — 2004
2. •
   (humorous, rare) Something that is plump.