Webster Dictionary, 1913
Century (Page: 233)
2. A period of a hundred years; as, this event took place over two
centuries ago. Century, in the reckoning of time, although often used in a
general way of any series of hundred consecutive years (as, a century of
temperance work), usually signifies a division of the Christian era,
consisting of a period of one hundred years ending with the hundredth year
from which it is named; as, the first century (a. d. 1-100 inclusive); the
seventh century (a.d. 601-700); the eighteenth century (a.d. 1701-1800).
With words or phrases connecting it with some other system of chronology
it is used of similar division of those eras; as, the first century of
Rome (A.U.C. 1-100).