The spelling of the word "moist tetter" is quite unusual and may be difficult to decipher. In IPA phonetic transcription, it is written as /mɔɪst ˈtɛtər/. The first part, "moist," is pronounced with the vowel sound /ɔɪ/ as in "boy" and the consonant cluster /st/. The second part, "tetter," is pronounced with the vowel sound /ɛ/ as in "bed" and the consonant cluster /tər/. Overall, the word is pronounced as "moy-st tet-er." It refers to a type of skin rash or infection.
Humid t.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.