Subordinators in English grammar are words including the function word that that introduce dependent or subordinate clauses including noun clauses, adjective clauses, and adverb clauses. Function words perform definite grammatical functions but lack definite lexical meaning.
Subordinator is a grammatical function.
The grammatical form that can function as the subordinator in English grammar is the subordinating conjunction.
The term noun clause marker is also used for subordinating conjunctions that introduce noun clauses. The term relative pronoun is also used for subordinating conjunctions that introduce adjective clauses.
Some subordinating conjunctions that function as subordinators include that, which, who, because, and after. (Note that many subordinating conjunctions perform other grammatical functions such as subject and direct object in addition to the grammatical function of subordinator.
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Hopper, Paul J. 1999. A short course in grammar. New York: W. W. Norton & Company.
Huddleston, Rodney. 1984. Introduction to the grammar of English. Cambridge: Cambridge University Press.