veretilla.

From veretrum (“penis; genitals”) + -lus (diminutive suffix). As it is first attested in Apuleius, it may have been a neologism coined by him, possibly intended as a translation of Greek βάλανος (bálanos, “glans, penis”), to refer to a type of shellfish that visually resembled a human penis. Editors differ on whether the passage where this word occurs should be read with feminine singular accusative "veretillam" or neuter singular accusative "veretillum", or even neuter plural accusative "veretilla". If the feminine form "veretillam" is correct, there is a change in gender from the neuter base word veretrum. In principle, such gender changes may proceed by means of mistaking neuter plural forms such as veretra/veretilla for nominative feminine singular forms; however, per Adams, veretrum was generally used in the singular, unlike similar euphemisms such as verenda, verendōrum, so this may be a less likely route of gender change for this word than for others. The vocalism in -ill- is uncommon for a diminutive built on a -ro-stem noun with assimilation of -rl- to -ll-: the expected formation would be in -ell-. Strodach suggests the form was possibly influenced by analogy with a diminutive pēnicillus, from pēniculus in the meaning "penis".