osto (2) noun "the gates of the Sun" (LT1:264; this "Qenya" word was probably obsoleted by # 1 above)
the gates of the sun
strong 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.