Take the tour ×  "plumb" as far as I know is a predominantly
American usage, as in "That was just plumb crazy!"  I thought
plumb meant some kind of weight in bricklaying or such like, so
how did it come to mean "absolutely"? What was its origin and
history?  Edit: After Callithumpian's answer, I have a little
addition:  Why is it a US usage chiefly, and why do not the
British use it as much?  share|improve this question In my
experience, Brits do in fact use plumb to mean "spot-on". Eg,
"that's plumb-perfect". A company comes to mind that is called
"plumb-something" (meaning perfect whatever-they-sell). HOWEVER
perhaps the expression "plumb crazy" is NOT used in UK (I'm not
sure), and THAT is why you say "less used in the UK". ie "plumb
crazy" is (perhaps) not used in the UK, but "plumb" meaning
spot-on, is indeed used. BTW a funny one in the UK (particularly
amongst builders) is "tits", again meaning "spot on." (So, you
finish installing a window .. you exclaim, "Tits." (!)) –  Joe
Blow Jun 15 '11 at 15:54 a