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.
1959 as a shortening of monophonic in reference to recordings; earlier used among printers for "monotype machine" (c. 1925) and generally for monochrome (motorcar, etc.), 1940s. From 1964 as short for mononucleosis.
<a href="https://www.etymonline.com/word/mononucleosis">Etymology of mononucleosis by etymonline</a>
Harper, D. (n.d.). Etymology of mononucleosis. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/mononucleosis