49. 1.  Nouns in -us, particularly in early Latin, often form the Genitive Singular in -i, following the analogy of nouns in -us of the Second Declension; as, senati, ornati.  This is usually the case in Plautus and Terence.

2.  Nouns in -us sometimes have -u in the Dative Singular, instead of -ui; as, fructu (for fructui).

3.  The ending -ubus, instead of -ibus, occurs in the Dative and Ablative Plural of artus (Plural), limbs; tribus, tribe; and in dis-syllables in -cus; as, artubus, tribubus, arcubus, lacubus.  But with the exception of tribus, all these words admit the forms in -ibus as well as those in -ubus.

4.  Domus, house, is declined according to the Fourth Declension, but has also the following forms of the Second:—­

domi (locative), at home; domo, from home; domum, homewards, to one’s home; domos, homewards, to their (etc.) homes

5.  The only Neuters of this declension in common use are:  cornu, horn; genu, knee; and veru, spit.

Exceptions to Gender in the Fourth Declension.

50.  The following nouns in -us are Feminine:  acus, needle; domus, house; manus, hand; porticus, colonnade; tribus, tribe; Idus (Plural), Ides; also names of trees (Sec. 15, 2).

* * * * *

FIFTH DECLENSION.

e-Stems.

51.  Nouns of the Fifth Declension end in -es, and are declined as follows:—­

Dies, m., day.                Res, f., thing. 
SINGULAR.        PLURAL.          SINGULAR.        PLURAL.
Nom.  dies            dies            res             res
Gen.  diei            dierum          rei             rerum
Dat.  diei            diebus          rei             rebus
Acc.  diem            dies            rem             res
Voc.  dies            dies            res             res
Abl.  die             diebus          re              rebus

Peculiarities of Nouns of the Fifth Declension.

52. 1.  The ending of the Genitive and Dative Singular is -ei, instead of -ei, when a consonant precedes; as, spei, rei, fidei.

2.  A Genitive ending -i (for -ei) is found in plebi (from plebes = plebs) in the expressions tribunus plebi, tribune of the people, and plebi scitum, decree of the people; sometimes also in other words.

3.  A Genitive and Dative form in -e sometimes occurs; as, acie.

4.  With the exception of dies and res, most nouns of the Fifth Declension are not declined in the Plural.  But acies, series, species, spes, and a few others are used in the Nominative and Accusative Plural.

Gender in the Fifth Declension.

53.  Nouns of the Fifth Declension are regularly Feminine, except dies, day, and meridies, mid-day.  But dies is sometimes Feminine in the Singular, particularly when it means an appointed day.