Tarumbar noun; apparently "King of the World" (possibly an ephemeral form): this would be tár "king" (q.v.) + umbar as a variant of Ambar "world".
king of the world
proper name. King of the World
A title of assumed by Morgoth when he lay claim to the world in Silmarillion revisions from the 1950s-60s (MR/121), but not appearing in the published version of The Silmarillion. This name is a compound of tar- “king” and Ambar “World”, the second element appearing in its rarer alternate form: Umbar (see PE17/105).
Conceptual Development: The title was first written as (rejected) Aran Endór “King of Middle-earth”.
Word Gloss tar- “high, high; [ᴹQ.] king or queen (in compounds)” Ambar “The World, Earth, (lit.) Habitation, Settlement”
ambar (2) noun "fate, doom" (variant of umbar?) in Turambar (SA:amarth); stem ambart- (PE17:66), instrumental ambartanen "by doom" (Silm ch. 21, UT:138, PE17:66). The early "Qenya" lexicon has ambar "Fate", also amarto (LT2:348)
ambar (1) ("a-mbar") noun "oikumenē [Greek: the earth as the human habitation], Earth, world" (MBAR), stem ambar- (PE17:66), related to and associated with mar "home, dwelling" (VT45:33); in VT46:13 the latter glosses are possibly also ascribed to the word ambar itself (the wording is not clear). The form ambaren also listed in the Etymologies was presumably intended as the genitive singular at the time of writing (in LotR-style Quenya it would rather be the dative singular); in the printed version in LR, the misreading "ambaron" appears (see VT45:33). Ambar-metta noun "the end of the world" (EO); spelt ambarmetta in VT44:36. The element #umbar in Tarumbar "King of the World" (q.v.) would seem to be a variant of ambar, just like ambar #2 "doom" also alternates with umbar (see below).
umbar (umbart-, as in dat.sg. umbarten) noun "fate, doom" (MBARAT), also name of tengwa #6 (Appendix E).Cf. Umbarto. In the pre-classical Tengwar system presupposed in the Etymologies, umbar was the name of letter #18 (VT45:33), which tengwa Tolkien would later call malta instead changing its Quenya value from mb to m. In the word Tarumbar "King of the World" (q.v.), umbar appears to be a variant of Ambar (q.v.) instead.
marta (3) noun "fate" (VT45:33, VT46:13) Cf. marto.
amarto noun "Fate" (also ambar) (LT2:348; in LotR-style Quenya rather umbar, umbart-)