noun
subject complement
A grammatical term for a complement that describes or identifies the subject, typically following a copula.
「彼は医者だ」の「医者」は主格補語です。
In 'He is a doctor,' 'doctor' is a subject complement.
目的格補語 is an object complement, which describes or identifies the direct object, whereas 主格補語 describes the subject.
Compound of 主格 (nominative case) + 補語 (complement), a calque from English 'subject complement' or similar Western grammatical terminology.