μεσημέριον

From LSJ

ἐν δὲ μηνὸς πρῶτον τύχεν ἆμαρ → it chanced to be on the first of the month, that day fell on the first of the month

Source

Russian (Dvoretsky)

μεσημέριον: дор. μεσᾱμέριον Theocr. τό = μεσημβρινόν.