The quality or state of being calamitous; the degree of disaster or misfortune in a situation.
From 'calamitous' + '-ness' (state/quality). This nominalization converts the adjective into a noun describing the abstract quality of being disastrous.
The 'calamitousness' of an event—like the Titanic sinking—isn't just about what happened, but about how utterly unexpected and comprehensively catastrophic it turned out to be.
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