1640s, "relation to or consisting of 100 years," from Latin centenarius "of a hundred, relating to a hundred," from centenai "a hundred each," from centum "hundred" (see hundred).
As a noun, c. 1600 as "period of 100 years;" 1788 as "a hundredth anniversary, commemoration or celebration of a hundredth anniversary." The usual British word in this sense for the American centennial.
variant of suffix -an (q.v.), with connective -i-. From Latin -ianus, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective. In Middle English frequently it was -ien, via French.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dasa, Avestan dasa, Armenian tasn, Greek deka, Latin decem (source of Spanish diez, French dix), Old Church Slavonic deseti, Lithuanian dešimt, Old Irish deich, Breton dek, Welsh deg, Albanian djetu, Old English ten, Old High German zehan, Gothic taihun "ten."