Alien, alienable, inalienable—it's easy enough to see the Latin word alius, meaning "other," at the root of these three words. Alien joined our language in the 14th century, and one of its earliest meanings was "belonging to another." By the early 1600s that sense of alien had led to alienable, an adjective describing something you can give away or transfer to another owner. The word unalienable came about as its opposite, but so did inalienable, a word most likely borrowed into English on its own from French. Inalienable is the more common form today, and although we often see both forms used to modify "rights," it was unalienable that was used in the Declaration of Independence to describe life, liberty, and the pursuit of happiness.