Vis-à-vis comes from Latin by way of French, where it means literally "face-to-face." In English it was first used to refer to a little horse-drawn carriage in which two people sat opposite each other. From there it acquired various other meanings, such as "dancing partner." Today it no longer refers to actual physical faces and bodies, but its modern meaning comes from the fact that things that are face-to-face can easily be compared or contrasted. So, for example, a greyhound is very tall vis-à-vis a Scottie, and one currency may be stronger vis-à-vis another.