Predicate Nouns.—Nouns (substantival or adjectival) are often used as complements to the predicate. Thus,
a. A predicate substantive is a substantive forming part of the predicate and asserting something of its substantive: Περικλῆς ᾑρέθη στρατηγός
εἵλεσθε ἐκεῖνον πρεσβευτήν
b. A predicate adjective is an adjective forming part of the predicate and asserting something of its substantive: ὁ ἀνὴρ δίκαιός ἐστι
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].