accident
From LSJ
ὃ γὰρ βούλεται, τοῦθ' ἕκαστος καὶ οἴεται → what he wishes to be true, each person also believes to be true | what he wishes, each person also believes
P. and V. τύχη, ἡ, συμφορά, ἡ, P. περίπτωμα, τό, σύμπτωμα, τό.
in case of accident: P. ἤν τι συμβῇ.