Etymology

Wondering about the origin of the phrase 'plumb forgot'?

The word 'plumb' (pronounced 'plum') derives from the Latin 'plumbun (lead), the same word that 'plumber' derives from, because a plumber works (or used to) with lead pipes.

Since a plumb line is completely or absolutely perpendicular, the word 'plumb' became an adverb meaning 'completely or absolutely' in phrases like 'plumb forgot' or 'plumb crazy.'