Silent letters   The O in opossum is spelled but not pronounced It is a silent letter just like the H in the word honest The articles a and an are correctly based on the first pronounced letter not simply the first letter   So you have the phrase an honest man not a honest man even though H is a consonant Likewise the phrase should be a opossum not an opossum again based on the first pronounced letter   Therefore I will go through the Article changing an opossum to a opossum The O in opossum is no different from the H in honest