Definitions of plumb:

• noun:   the metal bob of a plumb line
• verb:   adjust with a plumb line so as to make vertical
• verb:   examine thoroughly and in great depth
• verb:   measure the depth of something
• verb:   weight with lead
• adjective:   exactly vertical

  Example: "The tower of Pisa is far out of plumb"

• adverb:   exactly

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

• adverb:   conforming to the direction of a plumb line
• adverb:   completely; used as intensifiers

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

• name:  A surname (rare: 1 in 50000 families; popularity rank in the U.S.: #6205)