The Collaborative International Dictionary of English v.0.48:
Septuagesima \Sep`tu*a*ges"i*ma\, n. [NL., fr. L. septuagesimus the seventieth, fr. septuaginta seventy.] (Eccl.) The third Sunday before Lent; -- so called because it is about seventy days before Easter. [1913 Webster]WordNet (r) 3.0 (2006):
Septuagesima n 1: the 3rd Sunday before Lent (or the 9th before Easter) [syn: Septuagesima, Septuagesima Sunday]