MaterDomini would be "mother of the Lord"
MaterDei would be "mother of God"
Dominicus = belonging to the Lord, a.k.a. "Dominic"
Dominici = 1st person genitive; "of Dominic"
mater = mother
Domingo is Spanish for Dominic -- it's also the name for Sunday, because it's "the Lord's (day)"
As an aside -- think about that: Spanish-speakers all over the world routinely call the first day of the week "The Lord's" instead of "Day of the Sun" like we English speakers. That goes for Spanish-speaking pagans, atheists, agnostics, you name it. The Catholic Faith is in their very language.
And of course there's "Adios" which means "A Dios" or "to God (with you)". The French have "Adieu" which means the same thing. I guess "Goodbye" could be a shortening of "God (be) by you".
Anyhow, I'm getting off topic.
I don't want to promote the off-topic-ness either, so I started a
new
thread...
In Vietnam everyone calls Sunday by the Chinese words that mean "The Lord's Day". Somewhat funny when used by the non-Catholic population.
...since this subject seems to have a certain appeal.. I did a quick search
and found some "very interesting things" (to quote +Fellay!) regarding
days of the week, domingo, the Lord's Day, and otherwise, that is,
Saturday (Sabbath/Sabado/Sabbat/7th Day) and, surprise, surprise,
feria, or weekdays...