Decline is correct for nouns and adjectives. The Romans (and for all I know the Greeks) imagines the basic form - the nominative, used for the subject of a sentence (ANNA bit Lucia) at the top of a perpendicular stick like a shadow stick. The other grammatical cases (accusative for the direct object, genitive for the possessive, dative for the indirect object, ablative for various prepositional meanings) were then said to decline or fall over in sequence! Very visual ... ANNA bit Lucia - nominative ANNA, stop biting your sister! (Vocative) Anna bit LUCIAM (Accusative. You can also say: Luciam bit Anna, with no ambiguity but with added emphasis - maybe Anne usually chomps Martha instead ...) Anna gave a bite LUCIAE (to Lucy = Dative = indirect object) Anna took the doll LUCIA (Ablative = by, with or in this case - from Lucy. In Latin it would actually need a separate preposition but the principle is the same. And the A in Lucia here is a long sound!)
Same in the plural; same in all five declensions. Aren't we lucky to live when we do!