What is a predicate nominative?
A predicate nominative is a noun that follows a linking verb and renames the subject. It is called a "predicate nominative" because it is a noun in the predicate. A predicate nominative is not a direct object, because it does not receive the action of the verb.
What is an intransitive verb?
A linking verb, by definition, has no action; therefore it cannot be followed by a direct object. While an action verb with a direct object is a transitive verb, a linking verb is called an intransitive verb.
Examples
1. Davida Malo was a writer and translator for the Hawaiian Court.
Subject: Davida Malo
Verb: was (an intransitive verb)
Predicate nominative: writer and translator (These are the other nouns naming Davida Malo.)
2. He met American missionaries in the court.
Subject: He (subjective pronoun)
Verb: met (action verb)
Direct object: American missionaries (This phrase receives the action of the verb "met"; "American missionaries" is not another term for Davida Malo, and so is not a predicate nominative.)