Meaning

noun an acute disease characterized by fever and swollen lymph nodes and an abnormal increase of mononuclear leucocytes or monocytes in the bloodstream; not highly contagious; some believe it can be transm

adjective designating sound transmission or recording or reproduction over a single channel

originUncertain. The Monache, a related ethnic group, seem to derive their name from the same common source as the Mono, as -chi occurs otherwise in the Yokutsan and Miwok languages as a relatively common suffix on tribal names.

Etymology from Wiktionary, CC BY-SA 3.0