monochrome

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

• noun A picture, especially a painting, done in different shades of a single color.
• noun The art or technique of executing such a picture.
• noun The state of being in a single color.
• noun A black-and-white image, as in photography or on television.

from The Century Dictionary.

• noun Painting or a painting in one color, which may, however, be relieved by the use of lighter and darker shades. Compare camaïeu and grisaille.
• Of one color; painted in one color; monochromic.

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

• noun A painting or drawing in a single color; a picture made with a single color.

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

• noun A black and white image, especially such a photograph.
• noun dated A painting executed in shades of a single colour.
• noun A ceramic glaze of a single colour; an object so glazed.
• adjective having only one colour
• adjective photography representing colours with shades of gray

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

• noun painting done in a range of tones of a single color
• noun a black-and-white photograph or slide
• adjective having or appearing to have only one color