That word would be disaster.
A synonym for the word "calamity" that starts with the letter "d" is "disaster." Both terms refer to significant and often sudden events that cause great damage, distress, or loss.
A disaster, like a calamity is a hugely problematic turn of events.
Boost is a synonym for the word lift and starts with the letter B.
calamity
disaster
starts
A thesaurus.
Disaster
A synonym starting with d of the word calamity is 'disaster'
hate
declared
Brighter.