103. Many nouns are defective in case-forms.1
a. Indeclinable nouns, used only as nominative and accusative singular.
fās, nefās, īnstar, nihil, opus (need), secus
Note 1— The indeclinable adjective necesse is used as a nominative or accusative.
Note 2— The genitive nihilī and the ablative nihilō (from nihilum nothing) occur.
b. Nouns found in one case only (monoptotes):
- In the nominative singular.
- In the genitive singular.
- In the dative singular.
dīvīsuī (m.) (cf. § 94.c)
- In the accusative singular.
vēnum (Dative vēnō in Tacitus)
- In the ablative singular
astū (m.) [by craft]
and many other verbal nouns in -us (§ 94.c).
Note— Māne is also used as an indeclinable accusative, and an old form mānī is used as ablative. Pondō with a numeral is often apparently equivalent to pounds. A nominative singular astus and a plural astūs occur rarely in later writers.
- In the accusative plural: īnfitiās.
c. Nouns found in two cases only (diptotes):
- In the nominative and ablative singular.
for, forte (f.)
- In the genitive and ablative singular.
spontis (rare), sponte (f.)
- In the accusative singular and plural.
dicam, dicās (f.)
- In the accusative and ablative plural.
forās, forīs (f.) (cf. forēs), used as adverbs.
d. Nouns found in three cases only (triptotes):
- In the nominative, accusative, and ablative singular.
impetus, -um, -ū (m.)2
luēs, -em, -ē (f.)
- In the nominative, accusative, and dative or ablative plural.
grātēs, -ibus (f).
- In the nominative, genitive, and dative or ablative plural.
iūgera, -um, -ibus (n.); iūgerum, etc., in the singular (cf. § 105.b)
e. Nouns found in four cases only (tetraptotes): the genitive, dative, accusative, and ablative singular.
diciōnis , -ī, -em, -e (f.)
f. Nouns declined regularly in the plural, but defective in the singular:
- Nouns found in the singular, in genitive, dative, accusative, ablative.
frūgis, -ī, -em, -e (f.)
opis, -ī (once only), -em, -e [nominative Ops (f.) as a divinity]
- Nouns found in the dative, accusative, ablative.
precī, -em, -e (f.)
- Nouns found in the accusative and ablative.
cassem, -e (f.)
sordem, -e (f.)
- Nouns found in the ablative only.
obice (m. / f.).
g. Nouns regular in the singular, defective in the plural.
- The following neuters have in the plural the nominative and accusative only.
iūs broth (iūra)
tūs or thūs (tūra)
Note— The neuter iūs (right) has only iūra in classical writers, but a very rare genitive plural iūrum occurs in old Latin.
- calx, cor, cōs, crux, fax, flex, lane, lūx, nex, ōs (ōris),3 os (ossis),4 pāx, pix, rōs, sāl, sōl, vas (vadis), lack the genitive plural.
- Most nouns of the 5th declension lack the whole or part of the plural (see § 98.a).
h. Nouns defective in both singular and plural:
- Noun found in the genitive, accusative, ablative singular; nominative, accusative, dative, ablative plural.
vicis, -em, -e; -ēs, -ibus
- Noun found in the genitive, dative, accusative, and ablative singular; lacking the genitive plural.
dapis, -ī, -em, -e; -ēs, -ibus5
2. The dative singular impetuī and the ablative plural impetibus occur once each.
3. The ablative plural ōribus is rare, the classical idiom being in ōre omnium (in everybody's mouth) etc., not in ōribus omnium.
4. The genitive plural ossium is late; ossuum (from ossua, plural of a neuter u- stem) is early and late.
5. An old nominative daps is cited.