the.com/mono

means A viral infection (mononucleosis) that leaves you exhausted, feverish, and sidelined for weeks, often spread through saliva.

from Short for 'mononucleosis,' itself built from Greek 'monos' (single) and 'nucleus' (Latin for 'little nut,' i.e. the cell's core) — because the illness floods the blood with an excess of a single type of white blood cell (monocytes) that have an unusually large, single nucleus. The clinical name is 20th-century medical Latin/Greek; the 'kissing disease' nickname came later, once doctors noticed how efficiently it spread through saliva among teenagers and young adults.