The word "most plumbous" is a rare term that means "most leaden", or heavy like lead. The spelling of the word is pronounced /ˈməʊst plʌm.bəs/ in IPA phonetic transcription. The "most" is pronounced with a long "o" sound, while "plumbous" is pronounced with a short "u" sound followed by a silent "b" and a lightly pronounced "s". The word is not commonly used in modern English, but it may be encountered in scientific or technical contexts.
The word plumbous is derived from the Latin word plumbum, which means lead. The term plumbous is an adjective form of plumb, and it refers to something that is related to or contains lead.
The word most is an intensifier used to emphasize the degree of the adjective plumbous. In this context, most plumbous means most lead-containing or containing the highest proportion of lead.
Overall, the etymology of the word most plumbous can be traced back to the Latin word plumbum and its adjective form plumbous.