IPA: /dɪˈzæstrəs/
KK: /dɪˈzæstrəs/
Causing great damage or suffering; very bad or unfortunate.
The storm had disastrous effects on the small town, leaving many homes destroyed.
Disastrous is formed from "dis-" (meaning apart or away) and "astrum" (from Latin, meaning star). The word originally referred to events that were considered to be caused by unfavorable stars, hence something that brings misfortune or calamity.
Think of 'dis-' meaning apart and 'astrum' relating to stars — this helps you remember that 'disastrous' refers to something that brings misfortune, as if the stars are not aligned in your favor.