before vowels myc-, word-forming element meaning "mushroom, fungus," formed irregularly from Latinized form of Greek mykēs "fungus, mushroom, anything shaped like a mushroom," a word of uncertain origin (Beekes doubts the traditional explanation that connects it to the source of mucus). The correct form is myceto- (mycet-).
word-forming element expressing state or condition, in medical terminology denoting "a state of disease," from Latin -osis and directly from Greek -osis, formed from the aorist of verbs ending in -o. It corresponds to Latin -atio.
<a href="https://www.etymonline.com/word/mycosis">Etymology of mycosis by etymonline</a>
Harper, D. (n.d.). Etymology of mycosis. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/mycosis