Bridget

You are very kind. How politely you point out my stupidity! I spotted my error whilst visiting a friend. I combined two bits of grammar.

Here are my lines as punishment:

nominative singular Dominus "Lord"
genitive singular Domini "Lord’s" or "of the Lord"
dative singular Domino "to or for the Lord"
accusative singular Dominum "Lord" (English objective case)
ablative singular Domino "by or with (etc.) the Lord"
vocative singular Domine "Lord" (direct address)

nominative plural Domini "Lords"
genitive plural Dominorum "Lords’ or "of the Lords"
dative plural Dominis "to or for the Lords"
accusative plural Dominos "Lords" (English objective case)
ablative plural Dominis "by or with (etc.) the Lords"

As you say - thank goodness we don't have to do all that in English!