§97. Gender in the Fifth Declension
All nouns of the Fifth Declension are Feminine, except diēs (usually M.), day, and merīdiēs (M.), noon.
a. Diēs is sometimes feminine in the singular, especially in phrases indicating a fixed time, and regularly feminine when used of time in general: as, cōnstitūtā diē, on a set day; longa diēs, a long time.
J. H. Allen and J. B. Greenough, New Latin Grammar (Boston: Ginn, 1903). Text provided under a CC BY-SA license by Perseus Digital Library, http://www.perseus.tufts.edu, with funding from the National Endowment for the Humanities.