doomsday

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Judgment Day.
• noun An anticipated or feared catastrophic event, especially one on a global scale.
• idiom (til/until) For all time; forever.

from The Century Dictionary.

• noun The day of the last judgment.
• noun Any day of sentence or condemnation.
• noun [capitalized] The Doomsday Book (see below), or a record similar to it, as the Exon Doomsday, contemporary with it, preserved in Exeter cathedral.

from the GNU version of the Collaborative International Dictionary of English.

• noun A day of sentence or condemnation; day of death.
• noun The day of the final judgment.
• noun See Domesday Book.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Concerned with or predicting future universal destruction.
• adjective Given to or marked by forebodings or predictions of impending calamity.
• adjective Capable of causing widespread or total destruction; doomsday weapon.
• noun The day when God is expected to judge the world; end times.
• noun judgement day; the day of the Final Judgment; any day of decisive judgement or final dissolution.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an unpleasant or disastrous destiny
• noun (New Testament) day at the end of time following Armageddon when God will decree the fates of all individual humans according to the good and evil of their earthly lives