My favorite is still defamacast, with only 289 Google hits reported (though the reported number becomes only 60 if one actually pages through the results). The word isn't that common in law, either — it's just a Georgia term — but what I like about it is that it purports to be just a normal English word, albeit one coined by Georgia courts. It's not some Latin phrase, or all-caps statutory abbreviation or agency identifiers, or some such. It looks like a word, but a highly uncommon one.
I just came across another such example, which might be even more interesting, since I'm not sure that it's a self-conscious coinage (the way "defamacast" surely was): "Graffitism," defined in the Columbus (Ohio) City Code as basically the act of writing graffiti. It's at 1020 Google hits reported, though the number becomes only 189 if one actually pages through the results; and, as with "defamacast," many of the results aren't even substantive uses of the term.
Any other examples? Again, they have to be words that are used as ordinary English words would be — not Latin, not proper nouns, not all-caps, or the like. And, to give a convenient if arbitrary cutoff, they shouldn't yield more than 10,000 Google hits initially reported. (Just by way of a benchmark, "burglariously" yields over 30,000 Google hits initially reported.)
UPDATE: I originally said "term," but I've now corrected this to "word" -- I'd like to focus on individual words, rather than phrases.