Dominical Letter, one of seven letters, A, B, C, D, E, F, G, used to mark the Sundays throughout the year, so that if A denote the first Sunday, it will denote all the rest, and so on with B, C, &c., till at the end of seven years A becomes the dominical letter again.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Dominica * Dominican Republic