Feminine active participle of an unused root meaning to hollow out; something hollowed (as a gate), i.e. Pupil of the eye -- apple (of the eye).
H892. babah
[בָּבָה] noun feminine only עֵינוֺ בָּבַת Zechariah 2:12 the apple of his eye (Aramaic ; בָּבָא gate ᵑ7 Esther 5:14; Thes below נבב to which Ges gives sense perforate, hence opening of eye; but compare Arabic pupil of eye, perhaps = Dozy49 babe, baby, bébé (imitating infant's prattle) i.e. child of the eye; see Hi St, Fl in ChWBi. 419 b; compare אישׁוֺן ?).