vanilla: [17] A vanilla pod is etymologically a ‘little vagina’. The word was borrowed from Spanish vainilla, a diminutive form of vaina ‘sheath’ (the pod was so named because of its sheath-like shape). Vaina was descended from Latin vāgīna ‘sheath’, which came to be jokingly applied to the ‘female reproductive passage’ – hence English vagina [17]. => vagina
vanilla (n.)
1660s, "pod of the vanilla plant," from Spanish vainilla "vanilla plant," literally "little pod," diminutive of vaina "sheath," from Latin vagina "sheath of an ear of grain, hull of a plant" (see vagina). So called from the shape of the pods. European discovery 1521 by Hernando Cortes' soldiers on reconnaissance in southeastern Mexico. Meaning "flavoring extracted from the vanilla bean" is attested by 1728. Meaning "conventional, of ordinary sexual preferences" is 1970s, from notion of whiteness and the common choice of vanilla ice cream.