Definitions of plum:

• noun:   any of numerous varieties of small to medium-sized round or oval smooth-skinned fruit with a single pit
• noun:   any of several trees producing edible oval smooth-skinned fruit with a single hard stone
• adverb:   exactly

  Example: "Fell plumb in the middle of the puddle"

• adverb:   completely; used as intensifiers

  Example: "I'm plumb (or plum) tuckered out"

• name:  A surname (rare: 1 in 100000 families; popularity rank in the U.S.: #13434)