chasma
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
Latin > English (Lewis & Short)
chasma: ătis, n., = χάσμα>,
I an opening of the earth, a chasm, abyss, Sen. Q. N. 6, 9, 2; Dig. 4, 4, 11; 50, 15, 4; 18, 6, 10.—
II A kind of meteor: sunt chasmata, cum aliquod caeli spatium desedit et flammam velut dehiscens in abdito ostentat, Sen. Q. N. 1, 14, 1; Plin. 2, 26, 26, § 96; Serv. ad Verg. A. 9, 20.