1530s, "one hundred" (of anything), from Latin centuria "group of one hundred" of things of one kind (including a measure of land and a division of the Roman army, one-sixteenth of a legion, headed by a centurion), from centum "hundred" (see hundred) on analogy of decuria "a company of ten."
Used in Middle English from late 14c. as a division of land, from Roman use. The Modern English meaning "period of 100 years," reckoned from any starting point, is attested from 1650s, short for century of years (1620s). Latin centuria was not used in the sense "one hundred years," for which saeculum was the word (see secular). The older, general sense is preserved in the meaning "score of 100 points" in cricket and some other sports. The century-plant (American aloe), 1843, was believed to bloom only after a century of growth.