Noun

1. The opposition or dissimilarity of things that are compared; ,
2. The act of distinguishing by comparing differences
3. A conceptual separation or distinction
4. The perceptual effect of the juxtaposition of very different colors
5. The range of optical density and tone on a photographic negative or print (or the extent to which adjacent areas on a television screen differ in brightness)

Verb

1. Put in opposition to show or emphasize differences
2. To show differences when compared; be different