§88. Fourth Declension
The Stem of nouns of the Fourth Declension ends in u-. This is usually weakened to i before -bus. Masculine and Feminine nouns form the nominative by adding s; Neuters have for nominative the simple stem, but with ū (long).
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.