Autonymy is considered to be universal component of natural languages, and as a crucial element of "the metalanguage inside a language". When language is used to explain the meaning of a word, it is an "autonymy" (i.e. a word that refers not to its signified but to itself, to the signifier).

adj. autonymous

http://semlab5.sbs.sunysb.edu/~rlarson/LOT(99)/Day02.htmld/
http://www.calstatela.edu/faculty/dpitt/CompIdioms.htm