complementizer

noun

com·​ple·​men·​ti·​zer ˈkäm-plə-mən-ˌtī-zər 

-(ˌ)men-

: a function word or morpheme that combines with a clause or verbal phrase to form a subordinate clause

Word History

Etymology

complement entry 1 + -ize + -er entry 2

First Known Use

1965, in the meaning defined above