Originally this was Robert the Strong, margrave of Neustria and missus dominicus for the Loire Valley.
From the en.wikipedia.org
He was originally a missus dominicus in Swabia.
From the en.wikipedia.org
Originally appointed ad hoc, a reform in 802 led to the office of missus dominicus becoming a permanent one.
From the en.wikipedia.org
It is Tachybaptus dominicus, so if taxonomists are correct in placement, then it would be more closely related to the Little Grebe than would the Pied-billed.
From the guardian.co.uk
More examples
Sunday: first day of the week; observed as a day of rest and worship by most Christians