Sunni (n.) Look up Sunni at Dictionary.com
1620s, from Arabic, "adherent of the Sunnah; Muslim who accepts the orthodox tradition as well as the Quran," from Sunna "traditional teachings of Muhammad" (not, like the Quran, committed to writing, but preserved from his lips by his disciples or founded on his actions), literally "way, custom, course, tradition, usage." Related: Sunnite.