plump
1. Well-rounded and full in form; chubby.
2. Abundant; ample: a plump reward.
plump is correct, but so is plum.
plum
1.a. Any of several shrubs or small trees of the genus Prunus, bearing smooth-skinned, fleshy, edible fruit with a single hard-shelled stone that encloses the seed. b. The fruit of any of these trees.
2.a. Any of several trees bearing plumlike fruit. b. The fruit of such a tree.
3. A raisin, when added to a pudding or cake.
4. A sugarplum.
5. A dark purple to deep reddish purple.
6. An especially desirable position, assignment, or reward: an ambassadorship granted as a political plum.