annual:  Annual comes, via Old French annuel, from annuālis, a late Latin adjective based on annus ‘year’ (perhaps as a blend of two earlier, classical Latin adjectives, annuus and annālis – ultimate source of English annals ). Annus itself may go back to an earlier, unrecorded *atnos, probably borrowed from an ancient Indo-European language of the Italian peninsula, such as Oscan or Umbrian.
It appears to be related to Gothic athnam ‘years’ and Sanskrit átati ‘go, wander’. The medieval Latin noun annuitās, formed from the adjective annuus, produced French annuité, which was borrowed into English as annuity in the 15th century. => annals, anniversary, annuity
late 14c., from Old French annuel (12c.) or directly from Late Latin annualem (nominative annualis), corresponding to Latin annalis as adjective form of annus "year," from PIE *at-no-, from root *at- "to go," on notion of "period gone through" (cognates: Sanskrit atati "goes, wanders," Gothic aþnam (dative plural) "year," Oscan akno- "year, holiday, time of offering"). Used of plants since 1710.