The following sometimes happens in the development of English language.
A phrase from a foreign language is imported into English. English speakers find the phrase useful, but long and cumbersome. They deal with it by dropping a part of it, and so reducing it to what seems to them to be a more manageable length. The dropped part is, however, essential to the meaning that the phrase has in the language of its origin; the shortened form of the phrase thus has a very different meaning in that language, or, sometimes, no meaning at all. In English, the shortened form of the phrase nevertheless continues to be used with the same meaning as the original, full-length one; that becomes established as its meaning in English.
Caffè latte thus became latte (even though in Italian that is a word for [unadorned] milk), chef de cuisine became chef (which is, in French, a term for somebody who heads an organisation of any kind, including those that have nothing to do with food preparation), maître d'hôtel became maître d' (literally 'master of', an incomplete expression), chaise longue became, at least in American English, chaise, and obiter dicta became dicta. An older example of what is essentially the same phenomenon can be seen in the shortening of omnibus to bus (which is, in Latin, a dative-forming suffix with no independent meaning).
Is there a term for this kind of a phenomenon? Note that the question is specifically about this shortening of foreign phrases, not about the broader phenomenon of foreign words acquiring in English different meanings from the ones they have in their languages of origin.