Of or relating to the hours before midday; belonging or appropriate to the morning or forenoon.
Before midday; in the morning; = ante meridiem . Now somewhat archaic.
Late 16th century; earliest use found in Thomas Hood (bap. 1556, d. 1620), mathematician and physician. From classical Latin antemerīdiānus occurring or done before noon from ante merīdiem before noon + -ānus.