"Mertes" is a seldom-used word, but its spelling can be explained through the International Phonetic Alphabet (IPA). The word is pronounced with three syllables: /ˈmɜrtɛz/. The first syllable is stressed, and the vowel sound is similar to the "er" in "her." The second syllable is pronounced with a short "e" sound, like the "e" in "met." The final syllable has a "z" sound and a short "e" sound. The unusual spelling does not have a clear origin, but it could stem from a surname or a regional dialect.