contrast

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To set in opposition in order to show or emphasize differences.
• intransitive verb To show differences when compared.
• intransitive verb Linguistics To evince a difference that can distinguish meaning.
• noun The act of contrasting; a setting off of dissimilar entities or objects.
• noun The state of being contrasted.
• noun A difference, especially a strong dissimilarity, between entities or objects compared.
• noun One thing that is strikingly dissimilar to another.
• noun The use of opposing elements, such as colors, forms, or lines, in proximity to produce an intensified effect in a work of art.
• noun The difference in brightness between the light and dark areas of a picture, such as a photograph or video image.
• noun Linguistics A difference between units, especially one that distinguishes meaning.

from The Century Dictionary.

• To set in opposition, as two or more objects of a like kind, with a view to show their differences; compare by observing differences of character or qualities: used absolutely or followed by with: as, to contrast two pictures or statues; to contrast the style of Dickens with that of Thackeray.
• In the fine arts, to exhibit the differences or dissimilitude of; heighten the effect of, or show to advantage, by opposition of position, attitude, form, or color.
• To stand in contrast or opposition; exhibit diversity on comparison.
• noun Opposition; dispute.
• noun Opposition in respect of certain qualities; antagonistic difference; direct opposition: as, the contrasts and resemblances of the seasons.
• noun Comparison by exhibiting the dissimilitude or the contrariety of qualities in the things compared; the placing of opposites together in order to make the antagonism of their qualities more apparent.
• noun In the fine arts, opposition of varied forms or colors, which by juxtaposition magnify the effect of one another's peculiarities.
• noun In psychological optics, the reciprocal induction of colors and brightnesses in the present field of regard.
• noun In psychology, generally, any supposed intensification or throwing into relief by juxtaposition with an opposite.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of contrasting, or the state of being contrasted; comparison by contrariety of qualities.
• noun Opposition or dissimilitude of things or qualities; unlikeness, esp. as shown by juxtaposition or comparison.
• noun (Fine Arts) The opposition of varied forms, colors, etc., which by such juxtaposition more vividly express each other's peculiarities.
• transitive verb To set in opposition, or over against, in order to show the differences between, or the comparative excellences and defects of; to compare by difference or contrariety of qualities.
• transitive verb (Fine Arts) To give greater effect to, as to a figure or other object, by putting it in some relation of opposition to another figure or object.
• intransitive verb To stand in opposition; to exhibit difference, unlikeness, or opposition of qualities.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable A difference in lightness, brightness and/or hue between two colours that makes them more or less distinguishable.
• noun uncountable The degree of this difference.
• noun countable A difference between two objects, people or concepts.
• noun countable A control on a television, etc, that adjusts the amount of contrast in the images being displayed.
• noun countable, uncountable, rhetoric Antithesis.
• verb transitive To set in opposition in order to show the difference or differences between.
• verb intransitive To form a contrast.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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 put in opposition to show or emphasize differences
• noun the opposition or dissimilarity of things that are compared
• noun the act of distinguishing by comparing differences
• verb to show differences when compared; be different
• noun the perceptual effect of the juxtaposition of very different colors
• noun a conceptual separation or distinction