[*** \mathrm{plumb}^1] |pləm|

source: How to plumb the depth when floatfishing a waggler — Angling Times

verb with object

1. measure (the depth of a body of water):

〈水深〉を測鉛で測る; …を測深する

e.g. I plumbed the depth and found the bottom of the shelf to be seven meters down.

no object, with adverbial (of water) be of a specified depth:

e.g. at its deepest the lake scarcely plumbed seven feet.

explore or experience fully or to extremes:

〈心など〉を奥底まで見抜く［探る］; …の真相を知る; …を測知する(fathom)

e.g. she had plumbed the depths of depravity.

2. test (an upright surface) to determine the vertical:

…を(垂直かどうか)下げ振りで調べる

e.g. they are valuable aids in plumbing the frames and keeping the side of the ship fair.

a plumb bob.

鉛錘（えんすい）; (水深測定用の)測鉛; (釣りの)おもり; 下げ振り

1. informal exactly:

｟くだけて｠ 正確に

e.g. a bassoonist who sits plumb in the middle of the wind section.

as submodifier North American to a very high degree; extremely:

｟米･くだけて｠ まったく

e.g. they must both be plumb crazy.

2. archaic vertically:

垂直に

e.g. drapery fell from their human forms plumb down.

vertical:

垂直の(vertical)

e.g. ensure that the baseboard is straight and plumb.

not exactly vertical:

e.g. the towers are inclined, from four to ten feet out of plumb.

Middle English (originally in the sense ‘sounding lead’): via Old French from Latin plumbum ‘lead’.

[*** \mathrm{plumb}^2] |pləm|

verb with object

install and connect water and drainage pipes in (a building or room):

〈家など〉に鉛管を敷設する

e.g. the house could not be plumbed at all.

(plumb something in) mainly British install an appliance and connect it to water and drainage pipes.

〈洗濯機など〉を水道管につなぐ(｟主に英｠ in)

late 19th century (in the sense ‘work as a plumber’): back-formation from plumber.