The Collaborative International Dictionary of English v.0.48:

Quadragesima \Quad`ra*ges"i*ma\, n. [L., fr. quadragesimus the
   fortieth, fr. quadraginta forty; akin to quattuor four. See
   Four.] (Eccl.)
   The forty days of fast preceding Easter; Lent.
   [1913 Webster]

   Quadragesima Sunday, the first Sunday in Lent, about forty
      days before Easter.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Quadragesima
    n 1: the first Sunday in Lent [syn: Quadragesima,
         Quadrigesima Sunday]