Etymology
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annual (adj.)
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."
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annual (n.)
c. 1400, originally "service commemorating the anniversary of a person's death," from annual (adj.) or from Late Latin annualem (nominative annualis). By 1680s as "plant that grows again or blooms every year," also as "annual literary publication."
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semi-annual (adj.)
also semiannual, 1775, from semi- + annual (adj.). Related: Semiannually.
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triannual (adj.)
1630s, from tri- + annual (adj.). Related: Triannually.
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annualize (v.)
in economics and finance, 1904; see annual (adj.) + -ize. Related: Annualized; annualizing.
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per annum 

"in each year, annually," c. 1600, Latin, "by the year," from per (see per) + annum, accusative singular of annus "year" (see annual (adj.)).

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biannual (adj.)
also bi-annual; "occurring every six months, twice a year," 1837; see bi- + annual (adj.). Distinguished in sense from biennial, but the distinction is etymologically arbitrary. Related: Biannually; bi-annually.
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s.a. 

"without date," an abbreviation of Latin sine anno "without a year," from sine "without" (see sans) + ablative of annus "year" (see annual (adj.)).

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Anno Hegirae 
Medieval Latin, "in the year of the hegira," the flight of Muhammad from Mecca, 622 C.E., from which Muslims reckon time; from ablative of annus "year" (see annual (adj.)) + genitive of hegira. Abbreviated A.H.
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