A noun for “air” or “the lower air”, derived from the same primitive form ᴹ✶wilwā as its Quenya equivalent ᴹQ. Wilwa (Ety/WIL). Here the [[ilk|initial [w] became [gw]]]. Furthermore, after the [[ilk|final [a] was lost]], the [[ilk|final [w] became [u]]] and then became [o], as suggested by Helge Fauskanger (AL-Ilkorin/gwelo).
Conceptual Development: In the Addenda and Corrigenda to The Etymologies, Carl Hostetter and Patrick Wynne indicated the Tolkien revised this form to gwelm at the same time as he change its primitive to ᴹ✶wilmā and the Quenya form to ᴹQ. Wilma (EtyAC/WIL). This entry keeps the earlier Ilkorin form gwelo because Tolkien never revised ᴹQ. Wilwa in the narratives of this period.
A noun glossed “flat, lowlying vale” (Ety/DAL). Helge Fauskanger pointed out that the gloss is ambiguous, and it may be that this word can also be used an adjective “flat” (AL-Ilkorin/dôl).