The word disaster comes from the Middle French désastre from the old Italian disastro, which in turn comes from the Greek pejorative prefix dis- (bad; Gr: δυσ-) + aster (star; Gr: ἀστήρ). So disaster lit. means "bad star" in Greek. The sense is astrological, of a calamity blamed on an unfavorable position of a planet.
Note: Some etymologize dis- from the Greek dis [twice, bis-, bi-; Gr.: δις] from dyo [the number two, duo; Gr.: δύο].
In modern Greek (Romeika):
a) asteri or aster: star [Gr: αστέρι or αστήρ]