Our Love of Euphemisms
So long as humans have had things to be discreet about, they’ve had names that furnish some rhetorical distance from the things themselves. "Penis, Latin for 'tail,' in Cicero’s time was put to work as a euphemism for the male sex organ," notes Keyes. (And just as some writers groused, in recent decades, that a former meaning of gay had been filched from them, Cicero complained that he could no longer call a tail a tail, now that the word meant something else.)
For modern Americans, of course, penis is just the scientifically correct name.