Noun
1. An entrance that goes into a canal or hollow organ. The vaginal orifice is an introitus. (wikipedia.org)
2. (Music)
A piece of music played before a mass; a musical introduction of any sort. (wiktionary.org)
3. The vaginal opening. (biology-online.org)
Word origin: From Latin intro, “within,” and ire, “to go,” hence, an orifice or point of entry to a cavity or space.