plumb

Exactly.

“fell plumb in the middle of the puddle”

Completely; used as intensifiers.

“I'm plumb (or plum) tuckered out”

The metal bob of a plumb line.

Adjust with a plumb line so as to make vertical.

Examine thoroughly and in great depth.

Measure the depth of something.

Weight with lead.

Exactly vertical.

“the tower of Pisa is far out of plumb”