SINGULAR CASES.
[590]. In the genitive, the uncontracted form -uis sometimes occurs: as, anuis, old woman (Ter.). A genitive in -tī is rather common: as, adventī, arrival; ōrnātī, embellishment (Ter.); senātī, senate. In the dative, -ū is regularly found for -uī in neuters and often in gender words.
PLURAL CASES.
[591]. In the genitive plural, a shorter form in -um is occasionally found: as, passum, steps (Plaut., Mart.); currum, chariots (Verg.); EXERCITVM. The quantity of the u and the origin of this ending are uncertain.
[592]. In the dative and ablative plural, the following retain -u-bus: acus, pin, needle, arcus, bow, partus, birth, tribus, tribe. The following have -u-bus or -i-bus ([28]): artūs, plural, joints, lacus, lake, portus, haven, specus, cave, genū, knee, verū, a spit. All other words have -i-bus only.
[593]. Other case forms are found in inscriptions, as follows:
G. -uos: SENATVOS; -ū ([66]) SENATV; -uus, in the imperial age ([29, 1]): EXERCITVVS. D. -uei ([29, 2]): SENATVEI. Ac. -u ([61]): MANV. Ab. -uu ([29, 1]): ARBITRATVV; -uō, once, by some thought to be for -ūd ([426]); MAGISTRATVO. Plural: N. -uus ([29, 1]): MAGISTRATVVS.
[594]. domus, house, F., has stems of two forms, domu- and domo- ([401]); it is declined as follows: N. domus, G. domūs, rarely domī, D. domuī or domō, Ac. domum, Ab. domō or domū, Locative domī, rarely domuī. Plural: N. domūs, G. domuum, later domōrum, D. and Ab. domibus, Ac. domōs, less commonly domūs.
[595]. Some other substantives have an -u- stem in some of their cases, and an -o- stem in others: see angiportus, arcus, caestus, colus, cornū, cornus, cupressus, fīcus, fretus, gelus, laurus, murtus, penus, pīnus, quercus, rīctus, tonitrus, in the dictionary.