(1):

(n.) An event producing a subversion of the order or system of things; a final event, usually of a calamitous or disastrous nature; hence, sudden calamity; great misfortune.

(2):

(n.) A violent and widely extended change in the surface of the earth, as, an elevation or subsidence of some part of it, effected by internal causes.

(3):

(n.) The final event in a romance or a dramatic piece; a denouement, as a death in a tragedy, or a marriage in a comedy.