The Collaborative International Dictionary of English v.0.48:
Plump \Plump\ (pl[u^]mp), a. [Compar. Plumper
(pl[u^]mp"[~e]r); superl. Plumpest.] [OE. plomp rude,
clumsy; akin to D. plomp, G., Dan., & Sw. plump; probably of
imitative origin. Cf. Plump, adv.]
1. Well rounded or filled out; full; fleshy; fat; as, a plump
baby; plump cheeks. --Shak.
The god of wine did his plump clusters bring. --T.
2. Done or made plump, or suddenly and without reservation;
blunt; unreserved; direct; downright.
After the plump statement that the author was at
Erceldoune and spake with Thomas. --Saintsbury.
[Webster 1913 Suppl.]