Folks these days don't use plumb bobs to build a cabinet.
You use a tool called a level when building a cabinet.
Which as I've pointed out previously in this thread is indiscriminate as to where you use it.
Your brain seems to have disconnected for a moment.
A level (the tool) is defined as "a device consisting of a sealed glass tube partially filled with alcohol or other liquid, containing an air bubble whose position reveals whether a surface
is perfectly level or plumb."
A level is also "a horizontal plane or line with respect to the distance above or below a given point."
Level means "having a flat and even surface without slopes or bumps."
You, in post #4279, gave these definitions (which I have formatted slightly for ease of reading) for vertical, plumb, and horizontally level, which I agree with.
vertical - at right angles to a horizontal plane
plumb - exactly vertical or true
horizontally level - being on a precise horizontal plane; parallel to or in the plane of the horizon or a base line
“a horizontal surface”
If a "level" (the tool) will always show whether a surface is level (a flat, even surface without slopes), then that level (a horizontal plane) is, by definition, 90 degrees (a right angle) from vertical.
With me so far?
Plumb line will ALWAYS be vertical, no matter where on earth it is.
That means a plumb line will always be at a right angle to a level surface.
A plumb line is a radial from the center of the earth.
No matter where on earth you go, a radial line will always go from the center of the earth through that plumb line, and any surface you make level will always be perpendicular to that radial, BY DEFINITION.
A level will always be indiscriminate where you use it BECAUSE it will ALWAYS show a horizontal plane that is perpendicular to the radial from the center of the earth.
If level was defined as you say as 90 degrees from a slanted/sloped radial a level would not work in both places.
It's not defined by that.
Level is defined by being 90 degrees from vertical.
The radial is ALWAYS vertical in the position it is in.
If you move two feet, you're at a different radial, and you base your measurements on the new radial, not the old one.
If you move 1000 miles, you're at a third radial. You don't base your measurements off the first or second radial, because then none of your surfaces would be level or vertical, they'd be off by however many degrees.
So when building a cabinet, base your definitions of vertical on where you're at, not what vertical is a thousand miles away.
However, if you're building the Golden Gate Bridge, you need to take into consideration what is vertical at either end of the bridge, and what vertical is at the location of the support towers, because it's so large.