Secle

Of a man's age, part he lives in his father's life-time, and part after his son's birth; and thereupon it is wont to be said that three generations make one secle, or hundred years in the genealogies.

Source: wiktionary

If on this principle we calculate back from this first secular epoch preserved in history, the beginning ot the second secle falls U.C. 78.

Source: wiktionary

Such a secular year therefore was probably the term assigned to the life of the gods, as the natural secle was to the life of man, the secular day to that of nations, the secular week to that of one human race. They taught, as we know historically, that the expiration of each secular day was announced by wonders and signs, intelligible to them. So was the close of every natural secle; ten of which, of unequal length, made up a great day. The signs by which each of these epochs had been foreshewn, were recorded in their history .

Source: wiktionary

So the haruspex Vulcatius announced that the comet which appeared shortly after the assassination of Julius Cæsar indicated the end of the ninth secle and the beginning of the tenth.

Source: wiktionary