From Longman Dictionary of Contemporary Englishplumbplumb1 /plʌm/ verb [transitive] 1 → plumb the depths (of despair/misery/bad taste etc)2 UNDERSTANDto succeed in understanding something completely SYN fathom Psychologists try to plumb the deepest mysteries of the human psyche. → plumb something ↔ in→ See Verb table
Examples from the Corpusplumb• Who can plumb and penetrate such a person?• The system easily plumbs into existing induction hoppers.• Much mystique surrounds this territory as nobody has yet plumbed its limitations or possibilities.• The government said today that consumer confidence in December plumbed its lowest level ever since consumer surveys started, in January 1987.• Dubus, in his essays, tries to plumb the feelings of women.plumbplumb2 adverb 1 [always + adverb/preposition] informalEXACT exactly The bullet hit him plumb between the eyes.2 American English informalVERY completely – often used humorously The whole idea sounds plumb crazy to me.
Examples from the Corpusplumb• Josefina and I were plumb about to lose it.• Gets out there with them statues, she gets plumb crazy.• I'm sorry. I plumb forgot.plumbplumb3 adjective technical 1 HORIZONTALVERTICALexactly upright or level2 → out of plumb
Examples from the Corpusplumb• The sides, or jambs, must also be straight, plumb and square with the sill.• A plumb bob is useful to check the alignment of the header with the sill.• Twittering song uttered in soaring display flight, followed by butterfly-like descent with wings raised and a final plumb drop.• If any walls appear to lean, check by going back to the nearest upper window and drop a plumb line down.• But again, as with the lintels, the union did not allow the bricklayers to use a plumb line.• The barometer had dropped like a plumb weight.Origin plumb1 (1500-1600) plumb “metal weight on a plumb line” ((13-21 centuries)), from Old French plomb “lead”, from Latin plumbum