452. #-us# and #-um# were originally #-os# and #-om#. But #-us# was used
in the earliest times, #-um# somewhat later, and both became prevalent
between 218 and 55 B.C. (107, _c_). After #u# or #v#, however, the #-os#
and #-om# were retained till toward 50 A.D. (107, _c_); also after #qu#;
but #-cus# and #-cum# often displaced #-quos# and #-quom# (157): as,
#equos#, #equom#, or #ecus#, #ecum#, _horse_; #antīquos#, #antīquom#, or
#antīcus#, #antīcum#, _ancient_. In the vocative #-e# was always used,
and is retained by Plautus in #puere#, _thou boy_.
453. Words in #-rus# with a long penult, as, #sevērus#, _stern_, and the
following substantives with a short penult are declined like #domimus#
(449):
erus, _master_
iūniperus, _juniper_
numerus, _number_
umerus, _shoulder_
uterus, _womb_
For adjective stems in #-ro-# with nominative #-rus#, see 615.
454. Masculine stems in #-ro-# preceded by a short vowel or a mute,
except those above (453), drop #-os# in the nominative, and have no
vocative: as, stem #puero-#, N. #puer#, _boy_ (111, _b_). Most
masculines in #-ro-# have a vowel before #r# only in the nominative
#-er# (111, _b_): as #agro-#, N. #ager#. But in compounds ending in
#-fer# and #-ger#, _carrying_, _having_, and the following, the vowel
before #-r# is a part of the stem, and is found in all the cases:
adulter, Līber, _paramour_, _Liber_
gener, socer, _son-in-law_, _father-in-law_
puer, vir, _boy_, _man_
līberī, vesper, _children_, _evening_
For #Mulciber#, #Hibēr#, and #Celtibē̆r#, see the dictionary; for
adjective stems in #-ro-# with nominative #-r#, see 616. Once #socerus#
(Pl.).
455. #nihilum#, _nothing_, usually drops #-um# in the nominative and
accusative, becoming #nihil# or #nīl#, and similarly #nōn#, _not_, may
be for #noenum#, _naught_ (99). #famul# is used for #famulus#, _slave_,
by Ennius and Lucretius, once each (111, _b_).
456. Substantives ending in #-ius# or #-ium# (but never adjectives),
have commonly a single #-ī# in the genitive singular: as,
#Vergilius#, G. #Vergílī# (87); #fīlius#, _son_, G. #fīlī#; #cōnūbium#,
_marriage_, G. #cōnūbī#.
457. Vergil has once a genitive #-iī#, #fluviī#, _river’s_. Propertius
has #-iī# two or three times; with Ovid, Seneca, and later writers,
#-iī# is common: as, #gladiī#, _of a sword_; even in proper names, which
were the last to take #-iī#: as, #Tarquiniī#; but family names almost
always retain a single #-ī#. Locatives have #-iī#: as, #Iconiī# (Cic.).
458. Proper names ending in #-āius#, #-ēius#, or #-ōius# have #-āī#,
#-ēī#, or #-ōī# in the genitive and vocative singular and nominative
plural, and #-āīs#, #-ēīs#, or #-ōīs# in the dative and ablative plural
(127, 7): as,
#Gāius#, G., V., and N. Pl. #Gāī#, D. and Ab. Pl. #Gāīs#; #Pompēī#,
#Pompēīs#; #Bōī#, #Bōīs#. In verse #-ēī# of the vocative is sometimes
made one syllable (120): as, #Pompe͡i#; #Volte͡i# (Hor.).