An Adûnaic name for Morgoth, perhaps coined by Sauron when he introduced the worship of the dark god to the Númenóreans, translated as “Lord” (SD/376). It is derived from the word ârû “king” and was sometimes used in a compound together with Morgoth’s true Adûnaic name: Arûn-Mulkhêr (SD/367). In other writings (SD/357) it was the original Adûnaic name of Morgoth before he fell to evil, but that hardly makes sense in the conceptual scenario of the later Silmarillion, in which Morgoth had already become evil before men awoke.
North Sindarin
arum
masculine name. Oromë
A noun translated as “lord” (SD/311, 428). This nouns wins the prize for “most inflected Adûnaic noun”, since we have declensions for this noun in both the draft Adûnaic grammar and the later grammar of Lowdham’s Report. As such, it is very helpful for comparing how the noun declensions changed as Tolkien developed Adûnaic grammar. For example, comparing its draft plurals bāri/bārim to its later plural bârî/bârîm indicate the draft plural was originally formed with a short rather than long i. There are a few lingering examples of this short-i plural in later writings (SD/247, 251).
Conceptual Development: In earlier writings the rejected name Kherû “Lord” (SD/376) indicates a possible earlier form of this noun; Kherû itself was changed to Arûn. A similar form reappears in later writings in the name Adûnakhôr “Lord of the West”: either akhôr or khôr “lord”. Whether or not this later word replaced bâr is unknown.