plumb

UK: /ˈplʌm/ US: /plʌm/ ,(plum)

WordReference Random House Learner's Dictionary of American English © 2025

plumb /plʌm/   n. [countable]

1. Building, Surveying a small mass of lead hung on a line and used to measure the depth of water or to make sure a line is straight up and down.

adj. 

2. true according to a plumb line;
   perpendicular.

adv. 

3. in a perpendicular direction.
4. exactly, precisely, or directly:
   The last shot landed plumb in the hole for a birdie.
5. Informal Terms completely or absolutely:
   He was plumb stupid.

v. [~ + object]

6. Building to test or adjust by a plumb line, so as to make (something) vertical.
7. to examine closely:
   to plumb the poem's meaning.

Idioms

8. plumb the depths of, [~ + object] to experience (something) fully:
   plumbed the depths of despair.

WordReference Random House Unabridged Dictionary of American English © 2025

plumb  (plum), n. 

1. Building, Surveying 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. Cf. plumb line. 
2. Idioms out of or off plumb, not corresponding to the perpendicular;
   out of true.

adj. 

3. true according to a plumb line;
   perpendicular.
4. Informal Terms downright or absolute.

adv. 

5. in a perpendicular or vertical direction.
6. exactly, precisely, or directly.
7. Informal Terms completely or absolutely:
   She was plumb mad. You're plumb right.

v.t. 

8. Building to test or adjust by a plumb line.
9. to make vertical.
10. Nautical, Naval Terms [Shipbuilding.] horn (def. 35).
11. Nautical, Naval Terms to sound with or as with a plumb line.
12. Nautical, Naval Terms to measure (depth) by sounding.
13. to examine closely in order to discover or understand:
    to plumb someone's thoughts.
14. Building to seal with lead.
15. Building to weight with lead.
16. Building to provide (a house, building, apartment, etc.) with plumbing.

v.i. 

17. Building to work as a plumber.

Also, plum (for defs. 3–7).

• Vulgar Latin *plumba, for Latin plumbum lead
• Anglo-French *plombe
• Middle English plumbe, probably 1250–1300

plumb′a•ble, adj. 
plumb′less, adj. 
plumb′ness, n. 
Synonyms

• 3. vertical, straight, square.

Plumb  (plum), n. 

1. Biographical J(ohn) H(arold), born 1911, British historian.

Collins Concise English Dictionary © HarperCollins Publishers::

plumb / plʌm/ noun

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)

adverb
also: plum

1. in a vertical or perpendicular line
2. (intensifier): plumb stupid
3. exactly; precisely (also in the phrase plumb on)

verb

1. (transitive) often followed by up: to test the alignment of or adjust to the vertical with a plumb line
2. (transitive) to undergo or experience (the worst extremes of misery, sadness, etc): to plumb the depths of despair
3. (transitive) 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

Etymology: 13th Century: from Old French plomb (unattested) lead line, from Old French plon lead, from Latin plumbum lead

ˈplumbable adjective