plumb

¹ American  

[pluhm] / plʌm /

noun

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.

---

adjective

1. true according to a plumb line perpendicular.

   Synonyms:

   square, straight, vertical

2. Informal. downright or absolute.

adverb

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.

verb (used with object)

1. to test or adjust by a plumb line.

2. to make vertical.

3. Shipbuilding. horn.

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.

verb (used without object)

1. to work as a plumber.

idioms

1. out of / off plumb, not corresponding to the perpendicular; out of true.

Plumb ² American  

[pluhm] / plʌm /

noun

1. J(ohn) H(arold), 1911–2001, British historian.

---

plumb British  

/ 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 )

---

adjective

1. informal (prenominal) (intensifier)

   a plumb nuisance

adverb

1. in a vertical or perpendicular line

2. informal (intensifier)

   plumb stupid

3. informal exactly; precisely (also in the phrase plumb on )

verb

1. 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

Other Word Forms

• plumbable adjective
• plumbless adjective
• plumbness noun
• replumb verb (used with object)
• unplumb adjective

Etymology

Origin of plumb

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

Explanation

To plumb a body of water, you measure its depth. To plumb a house, you connect all of its pipes. To make carpentry plumb, you get it exactly vertical. Originally, the verb plumb only meant “to measure the depth of water.” These days, if you “plumb the depths” of something, you go in deep for knowledge and experience: your Heidegger seminar may plumb the depths of German Existentialism like Jacques Cousteau plumbed the depths of the ocean.

Example Sentences

Amanda is enraptured with its aspirational luxury: “The house had that hush expensive houses do. Silence meant the house was plumb, solid, its organs working in happy harmony.”

From The Wall Street Journal • Mar. 4, 2026

The bit remains frustratingly shallow, when there’s so much opportunity to plumb what it means to seek solace in smoothies and faux spirituality.

From Los Angeles Times • Feb. 12, 2026

In effect, the complaint here invites the Journal’s lawyer to use interrogatories and depositions to plumb the entire relationship between the two men.

From Slate • Jul. 23, 2025

At the other end, Brown complemented her opening partner beautifully with a fiery spell of fast bowling that saw Beaumont plumb in front.

From BBC • Jan. 30, 2025

I change into some clothes and come back out to see Biddy near about to wring her hand plumb off her wrists.

From "Girls Like Us" by Gail Giles

Related Words

• delve
• explore
• fathom
• penetrate
• unravel