1711, "a low story between two higher ones in a building," from French mezzanine (17c.), from Italian mezzanino, from mezzano "middle," from Latin medianus "of the middle," from medius (from PIE root *medhyo- "middle"). Sense of "lowest balcony in a theater" recorded by 1913.
Proto-Indo-European root meaning "middle." Perhaps related to PIE root *me- (2) "to measure."
It forms all or part of: amid; intermediate; mean (adj.2) "occupying a middle or intermediate place;" medal; medial; median; mediate; medieval; mediocre; Mediterranean; medium; meridian; mesic; mesial; meso-; meson; Mesopotamia; Mesozoic; mezzanine; mezzo; mezzotint; mid (prep., adj.); middle; Midgard; midriff; midst; midwife; milieu; minge; mizzen; moiety; mullion.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit madhyah, Avestan madiya- "middle," Greek mesos, Latin medius "in the middle, between; from the middle," Gothic midjis, Old English midd "middle," Old Church Slavonic medzu "between," Armenian mej "middle."