Second great battle of the Wars of Beleriand, translated “Battle-under-Stars” (S/106), a combination of dagor “battle”, nu “under”, the plural in of the definite article i and finally the class plural giliath of gil “star”.
Conceptual Development: In Silmarillion drafts from the 1930s, this battle was first named N. Dagor-os-Giliath (SM/268, LR/117), revised to N. Dagor nuin Giliath later in these drafts (LR/119, 145). This later form was also used in the Silmarillion revisions from the 1950s-60s (WJ/17).
It occasionally appeared as Dagor-nui-Ngiliath in both the 1930s and 1950s (LR/249, WJ/113), with the plural article elided and the class-plural undergoing nasal mutation to ngiliath. This second formation is probably more typical Sindarin.
dagor (“battle”) + nu (prep. “under”) + in (pl. article) + gîl (“star”) + ath (collective plural suffix)