The spelling of the word "MATTUS" can be explained using the International Phonetic Alphabet (IPA). The first sound in "MATTUS" is /m/, which is a bilabial nasal. The following vowel sound is /æ/, a low front vowel. Then comes the sound /t/, a voiceless alveolar stop, followed by another /t/. The final sound is /ʌs/, which consists of an open-mid back unrounded vowel and a voiceless alveolar fricative. Together, these sounds make up the spelling of "MATTUS" in accordance with the IPA.