Exactly perpendicular; vertical.

examine thoroughly and in great depth Tellingly, Ms. Liao said she had great difficulty finding three actors willing to plumb their own personalities. — New York Times (Jun 1, 2011)

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

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 1 [..]

"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 plu [..]

n. A weight suspended by a line to test the verticality of something.

Exactly perpendicular; vertical.

(adj) exactly vertical(adv) completely; used as intensifiers(adv) conforming to the direction of a plumb line(adv) exactly(n) the metal bob of a plumb line(v) measure the depth of something(v) weight [..]

Exactly vertical and perpendicular.

Perfectly vertical, a term often used for the placement of doors and windows.

When the batsman is clearly LBW, even at full speed, he is said to be plumb in front.

Exactly perpendicular or vertical. Or, at right angles to the horizon or floor.

 Vertically straight up/down. As an installation term, it refers to the importance of making sure that the window sides are perfectly perpendicular to the earth. Profile

Vertically straight, in relation to a horizontally level surface.

Vertical.

Exactly vertical.

Vertical or verticality, measured using a plumb-line or plumb-rule or these days a spirit level.

truly vertical, as indicated by a plumb line (cricket) Describing an LBW where the batsman is hit on the pads directly in front of his wicket and should be given out.