Third declension adjectives of one termination have only one form for the nominative singular. The same form works for all three genders. The tricky part comes in the dictionary listing for them. Since third declension adjectives of one termination almost always have stem changes when they appear in any case other than the nominative singular, a dictionary can't just give you the nominative singular as it does for all other kinds of adjectives. If it did, there would be no way for you to know that the adjective ingē ns (“huge”), for example, changes to ingent– when you start putting endings on it. To get around this problem, a dictionary gives you the genitive singular form, which illustrates the stem change. Therefore, the listing for ingē ns is: ingē ns, ingentis.

Table 6-6 Third Declension Adjectives of One Termination: ingē ns, ingentis (“huge”)

The first form of the dictionary listing is the nominative singular for the masculine, feminine, and neuter genders. The second form is the genitive. The sole purpose of the second word in the entry is to inform you of the stem change. With this information, you know that ingentem montem (“huge mountain”) is the accusative singular from the nominative ingē ns mī ns.