I recently spent a little time reading up on the White Wolf's (new) World of Darkness setting, particularly Vampire: The Requiem. One of the vampire factions in that game is called the Lancea Sanctum. Being a bit of a language geek, this phrase caught my eye.
At first glance, it looks like a noun followed by an adjective. I don't actually know Latin, but I've read a little about the basics and there are some handy online tools to look up words and stuff. So... 'lancea' is a word for a type of lance or spear. It is a feminine noun. 'Sanctum', naturally, means sacred (as in sanctified). But here's the snag: '-um' is the usual ending for an adjective's neuter form, not the feminine.
As Wikipedia states: 'In Latin, adjectives must agree with the nouns they modify in case and number and gender.' This means that when you have a feminine noun, any adjective describing it should also be in the feminine form. So, as far as I, with my admittedly limited language skills, can tell, the phrase should actually be 'Lancea Sancta'.
OK, so before publishing this comment, I decided to still dig around a little in case I was mistaken somehow. On White Wolf's wiki I found a statement that the faction would have originally been called 'Lancea et Sanctum', i.e. the 'lance and sanctum'. The modern English meaning of 'sanctum' is a sacred (or private) place, which (as far as I can tell) is derived from ecclesiastic Latin. Grammatically this phrase then seems more justifiable.
However, removing one small word makes a world of difference. As I said at the start, it looks like a noun and an adjective, not like two nouns. There is just no good reason for omitting the 'et'. You wouldn't shorten the English translation to 'lance sanctum'. It simply wouldn't make any sense. I can't help thinking that the 'Lancea et Sanctum' version is someone's retrospective (and less than successful) attempt to fix a grammatical error. (Though I don't know the source of this version. I haven't read any publications beyond the main Vampire rulebook, and if that book offers a translation for the covenant's name, I've missed it.)
EDIT: I did a little more digging around and apparently the Lancea Sanctum sourcebook itself translates the name as 'sanctuary of the lance'. But this is still wrong. 'Lancea' is the nominative form, not the genitive. It is also normal (though not strictly necessary) to place defining words after the main word. So the correct translation for 'sanctuary of the lance' should probably be 'Sanctum Lanceae'.
Whatever the case is, there's one important piece of advice I would like to give to anyone working in the world of fiction: if you want to make use of a foreign language, please, take the effort to get it right!