The Collaborative International Dictionary of English v.0.48:
Calamity \Ca*lam"i*ty\n.; pl. Calamities. [L. calamitas, akin
to in-columis unharmed: cf. F. calamit['e]]
1. Any great misfortune or cause of misery; -- generally
applied to events or disasters which produce extensive
evil, either to communities or individuals.
Note: The word calamity was first derived from calamus when
the corn could not get out of the stalk. --Bacon.
Strokes of calamity that scathe and scorch the
soul. --W. Irving.
2. A state or time of distress or misfortune; misery.
The deliberations of calamity are rarely wise.
Where'er I came I brought calamity. --Tennyson.
Syn: Disaster; distress; affliction; adversity; misfortune;
unhappiness; infelicity; mishap; mischance; misery;
evil; extremity; exigency; downfall.
Usage: Calamity, Disaster, Misfortune, Mishap,
Mischance. Of these words, calamity is the
strongest. It supposes a somewhat continuous state,
produced not usually by the direct agency of man, but
by natural causes, such as fire, flood, tempest,
disease, etc, Disaster denotes literally ill-starred,
and is some unforeseen and distressing event which
comes suddenly upon us, as if from hostile planet.
Misfortune is often due to no specific cause; it is
simply the bad fortune of an individual; a link in the
chain of events; an evil independent of his own
conduct, and not to be charged as a fault. Mischance
and mishap are misfortunes of a trivial nature,
occurring usually to individuals. "A calamity is
either public or private, but more frequently the
former; a disaster is rather particular than private;
it affects things rather than persons; journey,
expedition, and military movements are often attended
with disasters; misfortunes are usually personal; they
immediately affect the interests of the individual."