Dear Dr. Boli: My sister is getting married in May, and she insists on having three Elvis impersonators for her bridesmaids. This, of course, has caused a heated argument in our family over the obvious question: viz., what is the proper plural of Elvis? —Sincerely, Miss Aralia Throttle, D.Litt.
Dear Madam: The answer depends on etymology. You will find that this principle holds true for most of the vital questions: when in doubt, turn to etymology, and you will find the answer. In this case, the ending -is is common to Latin and Greek. If it were a Greek term, the proper plural of Elvis would be Elvides. The letter V is not native to classical Greek, however, so the answer is probably to be sought from Latin. The most correct plural of Elvis would then be Elves. Make sure to pronounce both syllables, of course, or you will just sound silly.