plumb / plum
These are two different adjectives that are sometimes conflated, plumb (confusingly often spelled plum) and plum.
The first means direct, precise, or absolute. It comes from the noun plumb, meaning a lead ball attached to a string and used to determine a vertical line. Nowadays, this noun is often formed as plumb bob. The word comes to us from the Anglo-Norman plom and eventually from the Latin plumbum, or lead. From Cursor Mundi, written sometime before 1400:
Wit cord and plum, þai wroght sa hei. [It is also written as plumme and plumbe in various manuscripts.]
(With cord and plumb, they dug it quickly.)
Plumb can also be a verb meaning to measure a depth and plummet shares the same root.
Adjectival use dates to at around 1425 when it appears in the Laud Troy Book in the sense of vertically straight:
Hit was diked doun plum, That no man myȝth ther-ouer com.
(It was dug down plumb, That no man might there over come.)
Within a few centuries, the sense of directly, in any direction not just down, and precisely had developed. From Philemon Holland’s 1601 translation of Pliny’s Historie of the World:
The wind Septentrio that bloweth plumbe North, is far more daungerous and mischievous.
The sense of absolutely or completely appears at about the same time. From Thomas Hughes’ 1588 The Misfortunes of Arthur:
The mounting minde that climes the hauty cliftes...Intoxicats the braine with guiddy drifts, Then rowles, and reeles, and falles at length plum ripe.
The second adjective, plum, is a 20th century coinage denoting something desirable or to be coveted. It’s from the name of fruit, which was considered especially tasty. From the 4 April 1923 Daily Democrat of Woodland, California:
Most of the propaganda for recall and censure is from those who are losing fat, plum jobs from the stroke of Friend Richardson’s ax.
The name of the fruit goes back to Old English and shares a common Germanic root. It is commonly believed to be a borrowing from the Latin pruna, but the shift from pr- to pl- cannot be explained by known patterns of phonological change and there are various explanations for the shift from n to m.
(Source: Oxford English Dictionary, 3rd Edition)
Copyright 1997-2015, by David Wilton