annus mirabilis n.

late 14c., "appointed by the year;" c. 1400, "occurring or done once a year," from Old French annuel "yearly" (12c.) or directly from Medieval Latin annualis "yearly," corresponding to Latin annalis as adjective form of annus "year."

This is reconstructed to be from Proto-Italic *atno- "year" (compare Oscan akno- "year, holiday, time of offering"), from PIE *at-no- "which goes," also "a year" (as "going around"), suffixed form of root *at- "to go" (source also of Sanskrit atati "goes, wanders," atamana- "to travel, wander," atya- "steed, runner"). The root also has Germanic derivatives meaning "a year," such as Gothic aþnam (dative plural) "year."

c. 1300, merivelle, "a miracle; a thing, act, or event which causes astonishment," also "wonderful story or legend," from Old French merveille "a wonder, surprise, miracle," from Vulgar Latin *miribilia (source also of Spanish maravilla, Portuguese maravilha, Italian maraviglia), altered from Latin mirabilia "wonderful things," from noun use of neuter plural of mirabilis "wonderful, marvelous, extraordinary; strange, singular," from mirari "to wonder at," from mirus "wonderful" (see smile (v.)). A neuter plural treated in Vulgar Latin as a feminine singular. Related: Marvels. The Marvel comics brand dates to 1961.