Feminine from an unused root meaning to cover; dusk -- dark, twilight.
H5939. alatah
עֲלָטָה noun feminine thick darkness **< darkness, dusk, which suits both passages (Bevan, privately). (Late Hebrew עֲלָטָה (rare); according to BaES 5 transposes from Arabic [be cloudy]; darkness); — absolute ׳ע, attending sunset Genesis 15:17 (with verb masculine; AlbrZAW xv (1895), 325 KöSynt. § 350 e read הָֽיְתָה); ׳בַּע Ezekiel 12:7 ("" בָּעֶרֶב), 12:6; 12:12.
עֶלְיוֺן עֲלִיָּה, עִלִּי, עֱלִי, עֵלִי, see עלה. p. 750f
עֲלֵי see עַל. עַלְיָן עַלְיָה, see עלוז עלוה,.p.752