The Plural of Penis
The Straight Dope (http://www.straightdope.com/columns/)
A must read imho
September 28, 2004
What exactly is the plural of penis? I would say penises, but it seems
too simple and obvious. Is it penis, like deer, or maybe peni, like fungi?
–Sissy, Emerald Isle, NC
If you have more than one, you should be writing to Ripley’s and not to the
Straight Dope. Heck, Sissy, if you have even one, the ﬁrst thing you should do
is change your name to Buddy.
In this case, your ﬁrst instinct is a good one. The English-style plural is usually
acceptable and often preferred. When you don’t know what the Latin plural is
and don’t have a dictionary handy, you should choose the English-style plural
rather than try to guess. (Sometimes even dictionaries will steer you wrong;
see below). In your example, penises is a perfectly good plural of penis in English. Many people who deal with penises professionally use the Latin-style
plural penes instead. That’s ﬁne too, but even among urologists, penises seem
to predominate. Seems, rather. ”Penises” seems to predominate.
Guessing the plural of a Latin word is one of those things where a little learning
is a dangerous thing (but that’s still ”not one half so bad as a lot of ignorance,”
to quote Terry Pratchett). Those with entirely too much learning know that
Latin nouns are divided into ﬁve categories, called declensions. To ﬁgure out
the plural of a Latin noun without cheating (i.e., looking it up), it is necessary,
and often suﬃcient, to know which of the ﬁve declensions it belongs to. (There
are a few nouns, like virus, that don’t ﬁt neatly into any of the declensions, but
more on that later). For example, you mention peni as a possible plural of penis.
The -i ending is valid for forming the plural of second-declension Latin nouns
ending in -us, but of course that doesn’t apply to penis. Part of the problem is
that when unaccented, the singular endings -us and -is tend to be...