It is interesting to note how many old Spanish words are used in everyday speech. In fact, in Chile, fierro is frequently used instead of hierro for iron, denantes means something like just a little while ago and I am always touched when I read (not hear for the most part) the possessive pronoun vuestro instead of su as it has a classy ring to it.
Legal Spanish is no stranger to old expressions that are not commonly used by most people. So pena de... to mean "Under penalty of...", foja instead of hoja to mean page and the construction -se after an imperative verb form as in notifíquese and hágase are a few you can expect. Not to mention, of course, the frequent usage of Latin terms, which deserves a separate post altogether.
The other day I was stumped by a Guatemalan term: Escribano de Cámara y de Gobierno. According to the Velázquez Spanish-English English-Spanish Dictionary, an Escribano de Cámara is "the clerk of a high court of justice who is also a notary". Incidentally, notaries are known as escribanos in Argentina as well.
In turn, an escribano is a scribe, and I wonder if notaries of yore in the Spanish colonies of the New World had other duties in addition to notarizing documents. Even today, a notary public is a well-respected and oft-consulted figure in the Chilean legal and business worlds. In my research of this term, I came across this page on Spanish colonial terms. I found it fascinating, even for the sake of browsing, and I hope it will be of use to you as well. These archaic terms serve as a reminder that we are part of a continuum in which we are speaking and writing words that will be archaic and perhaps someday even lost to future generations.