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.
of recordings, broadcasts, etc., "not stereo, having only one output signal," 1958, coined to be an opposite of stereophonic; from mono- "single" + -phonic, from Greek phōnē "sound, voice," from PIE root *bha- (2) "to speak, tell, say." It was used earlier in music, "pertaining to a style of composition in which one voice-part predominates over the others" (opposed to polyphonic), by 1885.
1881 in biology, "the single or sole type of a species in its genus, a genus in its family, etc.;" 1882 in printers' arts, "a print from a picture painted on a metal plate" (only one proof can be made, as the picture is transferred to the paper); 1893 as a brand name of typesetting machine; see mono- + type. Related: Monotypic (1878 in the biological sense)
D. Harper. “Etymology of mono.” Online Etymology Dictionary. https://www.etymonline.com/word/mono (accessed $(datetime)).
Definitions of mono
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 transmitted by kissing;