The 4th phrase of the Lament of Akallabêth (SD/247). One major conceptual change from earlier versions was that the subject of the sentence was plural Bârim an-Adûn (“Lords of the West”) instead of the earlier singular Bârun an-Adûn (“Lord of the West”). It seems that Tolkien decided that the drowning of Númenor was attributed to all of the Valar rather than just Manwë. A similar change from singular to plural was made in the corresponding Quenya sentence: herunūmen >> númeheruvi.
The subject Bârim of this sentence is the subjective plural of bâr “lord”. It is modified by the adjectival phrase an-Adûn “of the West”, with the genitive prefix an- “of” added to the noun adûn. The verb has the 3rd-plural suffix yu- “they”. In the grammatical rules of Lowdham’s Report this makes the subject emphatic, with a meaning more like “It was the Lords of the West who broke the Earth...” (SD/429).
The base sentence is modified by the prepositional phrase sâibêth-mâ Êruvô “with assent from Eru”. The combination sâibêth-mâ is the word sâibêth “assent” and the prepositional suffix -mâ “with”. The final word Êruvô is the name Êru and the prepositional suffix -ô “of”, with the usual glide-consonant [w] (which was sometimes written “v” as mentioned on SD/434) between the u and the following suffix.