annus mirabilis

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A year notable for disasters or wonders; a fateful year: "Hungary's blood bath was the saddest event in that annus mirabilis” ( C.L. Sulzberger).

Century Dictionary and Cyclopedia

1. A wonderful year. Specifically applied in English history, as in Dryden's poem of this title, to the year 1666, which is memorable for the great fire of London, for a victory of the British arms over the Dutch, etc.

Wiktionary

1. n. Any given year that undergoes a multitude of significant and fateful events, be they disasters or successes.