Quinquagesima
Concise Oxford English Dictionary © 2008 Oxford University Press:
Quinquagesima /ˌkwɪŋkwəˈdʒɛsɪmə/
▶noun the Sunday before the beginning of Lent.
– origin from med. L., fem. of L. quinquagesimus ‘fiftieth’, on the pattern of Quadragesima (because it is fifty days before Easter).
'Quinquagesima' also found in these Oxford entries:

