Plum vs. plumb
Plum is an adjective meaning desirable, and it also denotes the sweet, purplish fruit. The adjectival meaning originated as a figurative extension of the fruit.
Plumb is a verb meaning (1) to determine the depth of, to probe, or (2) to work as a plumber; an adjective/adverb meaning (3) exactly vertical, (4) utterly, or (5) squarely; and a noun referring to (6) a weight on the end of a line, used to determine water depth.
Examples
Plum
Despite crashing a Citroen World Rally Car in his two works outings this year – in Finland and Australia – Kris Meeke has landed the plum job in the French team. [RallySport Magazine]
Women miss out on plum overseas postings. [Financial Review]
The Premier put forward the husband of a close political ally for a plum role chairing a government-owned company. [Courier Mail]
Plumb
Though plumb in the centre of Europe, Budapest, for me, always casts a hypnotic east-meets-west spell, thanks to its years under Ottoman rule. [Telegraph]
Mr Page admits, researchers used to focus too much on thinking. Now Millward Brown is as keen as anyone to plumb consumers’ instincts. [Business Insider Australia]
The architecture had been all wrong, everything was out of plumb. [The Canberra Times]