The predicate is the word that supplies the action or state to the sentence. It is a verb. Sometimes the terms "verb" and "predicate" are used as synonyms because verbs are generally predicates (at least, all finite verbs are). We cannot as freely use the terms "subject" and "noun" as synonyms, for though nouns may be subjects, they may be many other things. Verbs, however, are predicates--that is their role. No confusion results, then, from the use of these terms interchangeably.