Sanskrit uṣas is an s-stem, i.e. the genitive case is uṣásas. It is from PIE*h₂ausos-, cognate to Greek Eos and Latin Aurora.
Ushas is an exalted goddess in the Rig Veda but less prominent in post-Rgvedic texts. She is often spoken of in the plural, "the Dawns." She is portrayed as warding off evil spirits of the night, and as a beautifully adorned young woman riding in a golden chariot on her path across the sky. Due to her color she is often identified with the reddish cows, and both are released by Indra from the Vala cave at the beginning of time.
Twenty of the 1028 hymns of the Rig Veda are dedicated to the Dawn: Book 7 has seven hymns, books 4–6 have two hymns each, and the younger books 1 and 10 have six and one respectively. In RV 6.64.1-2 (trans. Griffith) Ushas is invoked as follows:
The radiant Dawns have risen up for glory, in their white splendour like the waves of waters. She maketh paths all easy, fair to travel, and, rich, hath shown herself benign and friendly.
We see that thou art good: far shines thy lustre; thy beams, thy splendours have flown up to heaven. Decking thyself, thou makest bare thy bosom, shining in majesty, thou Goddess Morning.
In the "family books" of the Rig Veda (e.g. RV 6.64.5), Ushas is the divine daughter—a divó duhitâ —of Dyaus Pita "Sky Father." This is taken literally in the traditional genealogies of Hindu mythology.
In one recent Hindu interpretation, Sri Aurobindo in his Secret of the Veda, described Ushas as "the medium of the awakening, the activity and the growth of the other gods; she is the first condition of the Vedic realisation. By her increasing illumination the whole nature of man is clarified; through her [mankind] arrives at the Truth, through her he enjoys [Truth's] beatitude."