stain [OFr, desteindre, to dye] , 1. n., a pigment, dye, or substance used to impart color to microscopic objects or tissues to facilitate their examination and identification. Kinds include acid-fast stain, Gram’s stain, Wright’s stain. 2. v., to apply pigment to a substance or tissue to examine it under a microscope. 3. n., an area of discoloration.
