For the more pedantic people here, such as myself, the proper form of the plural of "copula" would probably "copulae", since it's a Latin noun. Do we add this? Fyrius 15:51, 5 December 2008 (UTC)
The Latin word 'copula' can hardly be derived from Arabic, for two reasons:
1. This word already appears in Old Latin (e.g. Plautus), and Arabic had zero influence on Latin at that time. In fact, Arabic was probably used in a very limited geographical area at that period. The only semitic languages that are known to have had some direct influence on Old Latin belong to the Canaanite branch of the family, and I guess Punic would be the most prominent here.
2. We don't know how the Arabic spoken 800 years before the Hijra was like (which is all the more reason not to assume Arabic origin), but the earliest Arabic we do know about had already transformed the Proto-Semitic /p/ to an /f/. Thus it cannot be the source of the word copula. Languages from the Canaanite branch have kept it until this very day, and though Hebrew (and maybe other Canaanite languages, but I doubt that Punic ever got into it) has also morphed it into an /f/ later in intervocalic positions, this happened quite late, well after the period of Old Latin.
Since the claim for Arabic origin was unsourced and seemed like original research, I removed it. My explanations are also original research, but he burden of proof does not rest on my shoulders.
As for the claim for Semitic origin, I find it possible, but not highly likely, and there's no respectable source to cite. The only source I could find is Black Athena: The linguistic evidence, and since this book could be said to have a clear agenda, it's somewhat less trustworthy than the plethora of dictionaries that mention nothing about it (and the book's agenda might have something to say about that too, of course ;)). Note that unlike what this book says, the Indo-European explanation has a very clear explanation for "the /l/". If the stem is "cop-" from "co(n) + apio", the suffix "-ula" is just the standard feminine diminutive suffix Latin when creating so many words, and like diminutives in most languages it's not shy of taking part in clearly non-diminutive uses.