• synonyms


  1. a small mass of lead or other heavy material, as that suspended by a line and used to measure the depth of water or to ascertain a vertical line.Compare plumb line.
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adjective Also plum.
  1. true according to a plumb line perpendicular.
  2. Informal. downright or absolute.
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adverb Also plum.
  1. in a perpendicular or vertical direction.
  2. exactly, precisely, or directly.
  3. Informal. completely or absolutely: She was plumb mad. You're plumb right.
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verb (used with object)
  1. to test or adjust by a plumb line.
  2. to make vertical.
  3. Shipbuilding. horn(def 32).
  4. to sound with or as with a plumb line.
  5. to measure (depth) by sounding.
  6. to examine closely in order to discover or understand: to plumb someone's thoughts.
  7. to seal with lead.
  8. to weight with lead.
  9. to provide (a house, building, apartment, etc.) with plumbing.
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verb (used without object)
  1. to work as a plumber.
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  1. out of/off plumb, not corresponding to the perpendicular; out of true.
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Origin of plumb

1250–1300; Middle English plumbe, probably < Anglo-French *plombe < Vulgar Latin *plumba, for Latin plumbum lead
Related formsplumb·a·ble, adjectiveplumb·less, adjectiveplumb·ness, nounre·plumb, verb (used with object)un·plumb, adjective
Can be confusedplum plumb

Synonyms for plumb

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for unplumb


  1. a weight, usually of lead, suspended at the end of a line and used to determine water depth or verticality
  2. the perpendicular position of a freely suspended plumb line (esp in the phrases out of plumb, off plumb)
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adjective Also: plum
  1. (prenominal) informal, mainly US (intensifier)a plumb nuisance
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adverb Also: plum
  1. in a vertical or perpendicular line
  2. informal, mainly US (intensifier)plumb stupid
  3. informal exactly; precisely (also in the phrase plumb on)
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  1. (tr often foll by up) to test the alignment of or adjust to the vertical with a plumb line
  2. (tr) to undergo or experience (the worst extremes of misery, sadness, etc)to plumb the depths of despair
  3. (tr) to understand or master (something obscure)to plumb a mystery
  4. to connect or join (a device such as a tap) to a water pipe or drainage system
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Derived Formsplumbable, adjective

Word Origin for plumb

C13: from Old French plomb (unattested) lead line, from Old French plon lead, from Latin plumbum lead
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for unplumb



"lead hung on a string to show the vertical line," early 14c., from Old French *plombe, plomee "sounding lead," and directly from Late Latin *plumba, originally plural of Latin plumbum "lead (the metal), lead ball; pipe; pencil," a word of unknown origin, related to Greek molybdos "lead" (dialectal bolimos) and perhaps from an extinct Mediterranean language, perhaps Iberian.

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early 15c., "to sink" (like lead), from plumb (n.). Meaning "take soundings with a plumb" is first recorded 1560s; figurative sense of "to get to the bottom of" is from 1590s. Related: Plumbed; plumbing.

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"perpendicular, vertical," mid-15c., from plumb (n.). The notion of "exact measurement" led to extended sense of "completely, downright" (1748), sometimes spelled plump, plum, or plunk.

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Online Etymology Dictionary, © 2010 Douglas Harper