Mignon Fogarty, better known as her alter ego Grammar Girl, has been sharing a series of short tips on usage and style. In her latest installment, she explains why the plural of the word ox is oxen instead of oxes.

Why do a few words take -en instead of -s or -es to become plural?

You may have heard that English is a Germanic language. The -en ending on plurals is something we get from our German roots. In Old English, some nouns were made plural with -s and -es as they are today, but many nouns took -en to become plural.

The s-form plurals became dominant in northern England first, while the en-form hung on in southern England. By the 14th century the s-form became dominant everywhere, but people didn’t let go of the en-form completely; as late as the 16th century the plural of eye was eyen and the plural of hose was hosen. Today only a few en-forms survive; the most common are oxen and children.