The story
Principal sense (female genitalia) introduced in the novel Vox by Nicholson Baker (1992); popularized as the title of the book Femalia, edited by Joani Blank (1993). Likely coined by Baker as a portmanteau of female and genitalia. Rare uses in other senses attested before 1992. The most general sense (anything pertaining to females or femaleness) may be derived by analogy to regalia; this sense, and this analogy, may also influence all the other, more specific senses.
Etymology from Wiktionary, CC BY-SA 4.0.