The plural of ox is oxen. This is an example of an irregular plural form in English. Unlike most nouns, which simply add an -s or -es to become plural, the word ox changes its ending to -en.
This irregular plural form has its roots in Old English, where the suffix -en was commonly used to denote plurals. Over time, this suffix became less common, and most nouns adopted the -s or -es ending. However, a few words, like ox, retained their older plural forms.
So, when referring to more than one ox, you should use the word oxen. For example: The farmer has ten oxen in his field.