Haurvatat and Ameretat are the last two of the seven Amesha Spentas, the emanations of God which Zoroastrians call the "Bounteous Immortals." They are not last in precedence, as there is no clearly defined hierarchy among the Seven, but they are last in that they are the latest to appear in the divine scheme of things. They are the virtues and gifts of the future, things devoutly to be hoped for, the signs of the Renewal at the End of Time.
The two Emanations, which are almost always referred to together, are both female in gender; this can be considered a result of linguistics, since the Avestan words Haurvatat (Wholeness) and Ameretat(Immortality) are of the female gender. But in the later thought of Zoroastrianism, in which the Bounteous Immortals become personified, these are indeed female entities.
"Haurvatat and Ameretat shall smite both hunger and thirst; Haurvatat and Ameretat shall smite the evil hunger and the evil thirst." (Zamyad Yasht, v.96, Darmesteter translation)