osto (2) noun "the gates of the Sun" (LT1:264; this "Qenya" word was probably obsoleted by # 1 above)
ostonoun. fortress, stronghold, strong place, *[ᴹQ.] city, *town with wall round
ostothe gates of the sun
ostostrong or fortified building or place, strong place, fortress
osto (1) noun "a strong or fortified building or place, strong place, fortress" (MR:350, 471; WJ:414); "city, town with wall round" (OS, VT46:8)
Túrosto place-name "Gabilgathol", a dwelling of the Dwarves (Sindarin Belegost; the names mean "Mickleburg", "Great Fortress"). Apparently túra + osto.