The latest Nuntii Latini mentions the Spanish constitution in relation to the Catalonian independence movement. It appears that in contemporary Latin a constitution is simply constitutio. Judging by the entry in L&S, the word constitutio had a roughly similar meaning (II.C) in classical Latin, too. Could someone explain what kind of "regulation", "order" or "arrangement" it means and how (if at all) it relates to the modern concept of a constitution? I found it puzzling, but my impression is that the modern English "constitution" is something much more specific than the classical Latin constitutio.
My reading of the Lewis and Short entry is that constitutio meant an imperial edict, and over time, came to mean any law. The excerpted text of Justinian says:
quodcumque ergo imperator per epistulam promulgavit, vel cognoscens decrevit, vel edicto praecepit, legem esse constat; hae sunt quae constitutiones appellantur.
The Online Etymology Dictionary entry for “constitution” says that the English word came from that sense of the Latin.
It’s possible that the semantic shift from “a law” to the modern meaning all occurred in English, and Neo-Latin writers just Latinized the English word “constitution”, ignoring the gap between the Roman and modern connotations.
First of all there is a classical verb - constituo constituere constitui constitutum which means set up, bring about, arrange, decide, decree and some others. There is a noun "constitutum -i" meaning, among others things, "an agreed arrangement". Looking at "constitutum" one can see that it is a second declension neuter noun and it does not end in "ium", so "constituto" is either ablative or dative case, singular. The meaning of the ablative case is "by", "with", or "from" and the dative meaning is "to". That is how case changes the meaning of the noun above. Refer to the Classical Oxford Latin Dictionary p.462. I hope this helps.