-es: Common Errors in English Usage Entry for Thursday, July 4, 2013

-es 
Latin-derived terms whose singular form ends in “-is” (like “thesis”) and whose plural forms end in “-es” (like “theses”) have the final syllables of their plural forms pronounced “eez.” This pattern causes some people to do the same with other words without a Latin singular “-is” form, like “processes” whose last syllable should properly be pronounced like “says.”