The Collaborative International Dictionary of English v.0.48:
Sext \Sext\, n. [L. sexta, fem. of sextus sixtt, fr. sex six: cf. F. sexte.] (R.C.Ch.) (a) The office for the sixth canonical hour, being a part of the Breviary. (b) The sixth book of the decretals, added by Pope Boniface VIII. [1913 Webster]WordNet (r) 3.0 (2006):
sext n 1: the fourth of the seven canonical hours; about noon