Definition 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
"The tower of Pisa is far out of plumb."
adverb: completely; used as intensifiers
"I'm plumb (or plum) tuckered out."
"Fell plumb in the middle of the puddle."
adverb: conforming to the direction of a plumb line