First and second declension adjectives

First-and-second declension adjectives are the first and commonest group of Latin adjectives. They borrow their feminine endings from the first declension and their masculine and neuter endings from the second, which is why the dictionary lists them in three forms, for example bonus, bona, bonum (good).

The idea is simple once you know those two noun families: to agree with a feminine noun the adjective uses first-declension endings, and to agree with a masculine or neuter noun it uses second-declension endings. So a single adjective can look like bona, bonus, or bonum depending on its noun.

Case	Masc.	Fem.	Neut.
Nom. sing.	magnus	magna	magnum
Gen. sing.	magnī	magnae	magnī
Acc. sing.	magnum	magnam	magnum

Examples:

• magnus servus - a big slave
• magna puella - a tall girl
• magnum bellum - a great war

Watch out for two things as an English speaker. The adjective's endings follow its own noun's gender, not its declension: poēta bonus (a good poet) keeps bonus masculine even though poēta looks first-declension, because the poet is masculine. And do not assume the adjective sits next to its noun; Latin often separates them, so match by gender, number, and case, exactly the endings this table shows.