Septuagesima
Charles Buck Theological Dictionary [1]
The third Sunday before the first Sunday in Lent; so called because it was about 70 days before Easter.
Webster's Dictionary [2]
(n.) The third Sunday before Lent; - so called because it is about seventy days before Easter.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature [3]
(seventieth), the third Sunday before Lent. The reason of its application to the day is uncertain. Some liturgical writers — e.g. Pamelius — trace it to the association of the ancient monastic Lent of seventy days with the seventy years' captivity of Israel in Babylon. The following is more probable: There being exactly fifty days between the Sunday next before Lent and Easter day inclusive, that Sunday is termed Quinquagesima, i.e. the fiftieth; and the two immediately preceding Sundays are called from the next round numbers Sexagesima, the sixtieth, and Septuagesima, the seventieth. The observation of these days and the weeks following appears to be as ancient as the time of Gregory the Great. Some of the more devout Christians observed the whole time from the first of these Sundays to Easter as a season of humiliation and fasting, though the ordinary custom was to commence fasting on Ash Wednesday. See Eden, Dict. of the Church, s.v.; Blunt, Dict. of Theology, s.v.