IPA: /ləˈmɛntəblɪ/
KK: /ləmˈɛntəblɪ/
In a way that expresses sadness or regret about something.
The project failed lamentably, leaving many disappointed.
Lamentably → It is formed from "lament" (from Latin "lamentari", meaning to mourn or express sorrow) and "-ably" (a suffix meaning in a manner). The word "lamentably" means in a manner that expresses sorrow or regret.
Think of expressing sorrow ('lament') in a certain way ('-ably') — that's why lamentably means to do something in a sorrowful manner.