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."

adverb: exactly

"Fell plumb in the middle of the puddle."

adverb: conforming to the direction of a plumb line