Stems in -υ, -ῡ

132.

133. a. Accented -υ at the end of the stem is made long in the nominative, accusative, and vocative singular, which in monosyllables are circumflexed.

b. In the accusative plural -ῦς probably results from dropping -ν- of the old ending -νς (cp. § 62.a and § 51.b).