What are the rules for making Latin words plural?
There are no rules governing the plural forms of Latin words. People have to learn which form to use as they see and use the word for the first time, and must become aware of any variations in usage that may exist. In cases where there is a choice between two possible plural forms of a certain word, most good dictionaries will list both plural forms. In many cases (but not always), the classical plural (the one based on the original Latin use of the word) is more technical, academic, or formal, and the other plural (formed by adding -s or -es), reflects the more common or popular usage. Several words that were borrowed into English from Latin no longer are used in their original singular forms. For example, the words datum and agendum are now extremely rare in English. Data is now commonly used as a singular, uncountable noun, and agenda has become a singular, countable noun (with the plural form agendas). With certain other Latin words, we use a different plural to convey a different
