114. Adjectives of the 3rd Declension are classified in this manner:

1. Adjectives of Three Terminations in the nominative singular (one for each gender).
   

   ācer, ācris, ācre

2. Adjectives of Two Terminations (masculine and feminine the same).
   

   levis (m. / f.), leve (n.)

3. Adjectives of One Termination (the same for all three genders).
   

   atrōx

a. Adjectives of two and three terminations are true i-stems and hence retain -ī in the ablative singular, -ia in the neuter plural, -ium in the genitive plural, and in the accusative plural regularly -īs (see §§ 73-74).¹

115. Adjectives of Three Terminations are declined as follows.

a.  The following stems in ri- are declined like ācer.

placer, campester, celeber, sequester, palūster, pedester, puter, salūber, silvester, terrester, volucer

So also names of months in -ber.

Octōber (cf. § 66)

Note 1— This formation is comparatively late, therefore, in the poets and in early Latin, either the masculine or the feminine form of these adjectives was sometimes used for both genders.

coetus alacris (Enn.)

In others, there is no separate masculine form at all, and these are declined like levis (see § 116 below).

faenebris, fūnebris, illūstris, lūgubris, mediocris, muliebris

Note 2— Celer, celeris, celere, swift, has the genitive plural celerum, used only as a noun, denoting a military rank. The proper name Celer has the ablative in -e.

116. Adjectives of Two Terminations are declined as follows.

Note— Adjectives of two and three terminations sometimes have an ablative in -e in poetry, rarely in prose.

117. The remaining adjectives of the 3rd declension are Consonant stems; but most of them, except Comparatives, have the following forms of i-stems:²

1. -ī in the ablative singular (but often -e).
2. -ia in the nominative and accusative plural neuter.
3. -ium in the genitive plural.
4. -īs (as well as -ēs) in the accusative plural masculine and feminine.

In the other cases they follow the rule for Consonant stems.

a. These adjectives, except stems in l- or r-, form the nominative singular from the stem by adding s.

atrōx (stem atrōc- + s)
egēns (stem egent- + s)³

b. Here belong the present participles in -ns (stem nt-).³

amāns, monēns

They are declined like egēns (but cf. § 121).

118. Adjectives of one termination are declined as follows.

119. Other examples are the following.

Note— Of these vetus is originally an s-stem. In most s-stems the r has intruded itself into the nominative also.

bi-corpor (for † bi-corps)
dēgener (for † dē-genes)

Footnotes