1140,
non "midday, 12 o'clock p.m., midday meal," from O.E.
non "3 o'clock p.m.," also "the canonical hour of nones," from L.
nona hora "ninth hour" of daylight, by Roman reckoning about 3 p.m., from
nona, fem. sing. of
nonus "ninth" (see
nones). Meaning shift from "3 p.m." to "12 p.m." began during 12c., when time of Church prayers shifted from ninth hour to sixth hour, or perhaps because the customary time of the midday meal shifted, or both. The shift was complete by 14c. (cf. same evolution in Du.
noen).
Noonday was first used by Coverdale (1535).