Ilúvatar masc. name "All-father", God (SD:401, FS, IL; Ilúv-atar, ATA, Iluvatar with a short u, SD:346). Often in combination with the divine name as Eru Ilúvatar, "Eru Allfather", cf. MR:112. "Qenya" genitive Ilúvatáren "of Ilúvatar" in Fíriel's Song, LR:47 and SD:246, the genitive ending is -en instead of -o as in LotR-style Quenya. Cf. the later genitive Ilúvataro in the phrase Híni Ilúvataro (see "Children of Ilúvatar" in the Silmarillion Index)
Quenya
ilúvatar
masculine name. Father of All
Ilúvatar
all-father
ilúvë
allness, the all
ilúvë noun "allness, the all". In Ilúvatar "All-father". _(SA; WJ:402, MR:471, IL) _In MR:355, ilúvë seems to be equated with Heaven. Cf. SD:401: Ilúvë Ilu "Heaven, the universe, all that is (with and without the Earth)".
A Quenya name for God (S/15, Let/155), translated “Father of All” or “All-father” (Let/204, MR/39). It is a compound of the noun ilúvë “all” and atar “father” (SA/atar, ilúvë; WJ/402).
Conceptual Development: This name dates back to the earliest Lost Tales (LT1/49), though ᴱQ. Ilúvatar originally meant “Sky Father” or “Heavenly Father” (LTA1/Ilúvatar, QL/42). A revised translation “Lord for Always” appeared in the Name-list for the Fall of Gondolin (PE15/27) and the translation “All-father” emerged in Silmarillion drafts from the 1930s (SM/78, LR/110). ᴹQ. Ilúvatar appeared in The Etymologies as the combination of ᴹQ. ilúve and ᴹQ. atar (Ety/ATA, IL).