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