1721, in reference to the system of musical notation devised by Guido d'Arezzo, who lived early 11c.
Entries linking to guidonian
Guido
masc. proper name, Italian, literally "leader," of Germanic origin (see guide (v.)). As a type of gaudy machoism often associated with Italian-Americans, 1980s, teen slang, from the name of character in Hollywood film "Risky Business" (1983).