Just thought of an alternative set of terms earlier today.
Now, I'd like to state that I'm one of those easily irritated folks who gets peeved to no end by "dorf", "clownite", "monies", and any number of other uselessisms. Basically the only term that I can remember actually liking somewhat was "Goblinite". Hell, I don't even use "Urist" as a catch-all, and I never name my dwarves McAnything.
Anyways, HFS. Personally, I'm a traditionalist sympathizer, so I believe that the original, official term of "HFS" (and I do believe that these features qualify as easter eggs, in a sense) is generally the most appropriate. It is, however, a rather generic term, and can occasionally fall victim to "Smurf Syndrome".
As an alternative to clownite, I considered the possibility of naming the materials based loosely on their properties.
Slade, being an incredibly hard material that is found in layers deep underneath the earth, would be termed "Hard Rock". I'm debating as to whether the temple or the pit should be called "the Hard Rock Café".
Adamantine is trickier... "Heavy Metal" doesn't really apply, since Adamantine is so light, but "Blues Metal" just doesn't seem to have the right ring to it.
What you call the demons, however, is beyond me. Patrons?
Like I said though, I still regard "HFS" as the official term.