Name of the “Great Sea” lying between Middle-earth and Valinor (S/37). This name is a compound of beleg “mighty” and gae(a)r “sea” (SA/beleg, gaer; PM/363).
Conceptual Development: In Silmarillion drafts from the 1930s, this name first appeared as N. Belegar (LR/14), soon revised to Belegaer (LR/19). In The Etymologies, it appeared as Belegoer (Ety/ÁLAT, AY, BEL), a reflection of Tolkien’s uncertainty on whether the diphthong [[n|[ai] became [oe] or [ae]]]. In the later Silmarillion revisions from the 1930s, he used Belegaer consistently following the [[n|revision of [oe] to [ae]]].
haloisi noun "the sea (in storm)", cf. haloitë (LT1:254)