A word have the same root (√ING) as the name Ingwë, giving a clue to the original meaning of that name. In a few places, the plural Ingar of this word was used as another name for the Vanyar (MR/230, 265), but Tolkien more frequently used the plural Ingwë for this purpose: see Ingwi.
In later writings, this word was generally presented as a noun meaning “top, highest point” (PM/340, VT47/28), but in the Etymologies, ᴹQ. inga was an adjective glossed “first”, as in “foremost” (Ety/ING).
Tolkien stated that “inga ... applied to shapes pointing upward” but also that it “referred primarily to position and could be used of tops relatively broad” (VT47/28). Therefore, inga referred to the highest level whether it was a single point or a plateau.