rogation
Concise Oxford English Dictionary © 2008 Oxford University Press:
rogation /rə(ʊ)ˈgeɪʃ(ə)n/
▶noun (in the Christian Church) a solemn supplication consisting of the litany of the saints chanted on the three days before Ascension Day.
– origin ME: from L. rogatio(n-), from rogare ‘ask’.
'rogation' also found in these Oxford entries:

