The etymology of vanilla is actually far from plain vanilla. The meaning of "plain" was first attested in the 1940s, when the whiteness and commonality of the ice cream flavor caused the new definition to arise. Before that, vanilla referred exclusively to the plant and extract of the plant, a term which was adopted in the 1660s from Spanish vainilla, which literally meant "little pod" (a word created during Hernando Cortes' infamous mission to the Aztec empire). This is a diminutive form of vaina, meaning "pod", and that derives from Latin vagina, meaning "sheath", under a connection of those pods having sheaths. Yes, that's right. It also had a secondary definition of "vagina" and is the etymon of our word for a woman's external genitals. Sort of makes sense, but what a wild twist that took. Vagina is reconstructed as having derived from Proto-Italic wagina, with the same meaning, and that likely comes from an unknown Proto-Indo-European root.
Adam Aleksic, a leading contender for valedictorian of his high school, is a 215-month-old boy with disturbing interests in etymology, vexillology, geography, and law. Adam would like to one day visit Tajikistan and probably isn't spying for the Uzbek government.
The Etymology Nerd