Yesterday, I was talking with spouse about the various words in English that come from the Latin word for lead: plumbum.
There’s plumber, plumb-bob, and vertical things being plumb. Probably other things too.
But I suddenly said to him, “I wonder if plum as in ‘plum crazy’ is another such word?”
So I just looked it up, and the answer is yes:
‘The notion of "exact measurement" led to the extended adverbial sense of "completely, downright" (1748), sometimes spelled plump, plum, or plunk.’