Complement

Complement - in grammar, a complement is a word, phrase, or clause that is necessary to complete the meaning of a given expression. Complements are often also arguments (expressions that help complete the meaning of a predicate).
Predicative, subject and object complements.
In many non-theoretical grammars, the terms subject complement and object complement are employed to denote the predicative expressions (such as predicative adjectives and nominals) that serve to assign a property to a subject or an object
Ryan is upset. – Predicative adjective as subject complement
Rachelle is the boss. – Predicative nominal as subject complement
That made Michael lazy. – Predicative adjective as object complement
We call Rachelle the boss. – Predicative nominal as object complement
This terminology is used in grammar books:^[4]

Type	Verb	Example	Elements
SV	intransitive	The sun is shining.	subject, verb
SVO	monotransitive	That lecture bored me.	subject, verb, object
SVC	copular	Your dinner seems ready.	subject, verb, subject complement
SVA	copular	My office is in the next building.	subject, verb, predicative complement
SVOO	ditransitive	I must send my parents an anniversary card.	subject, verb, indirect object, direct object
SVOC	complex-transitive	Most students have found her reasonably helpful.	subject, verb, object, object complement
SVOA	complex-transitive	You can put the dish on the table.	subject, verb, object, adverbial

However, this use of terminology is avoided by many modern theories of syntax, which typically view the expressions in bold as part of the clause predicate, which means they are not complements of the subject or object but rather are properties that are predicated of the subject or object.
The Cambridge Grammar of the English Language assigns the term "predicative complement" to both uses and shifts the terminological distinction to the verb:
Ed seemed quite competent: — complex-intransitive verb + predicative complement
She considered Ed quite competent : — complex-transitive verb + predicative complement

Complements are one of the five major elements of clause structure. The other four are subject, verb, object and adjunct (complements are in bold):

Both the brothers became doctors.