Source : WordNet®

Gram stain
     n : a staining technique used to classify bacteria; bacteria are
         stained with gentian violet and then treated with Gram's
         solution; after being decolorized with alcohol and
         treated with safranine and washed in water, those that
         retain the gentian violet are gram-positive and those
         that do not retain it are gram-negative [syn: {Gram's
         method}, {Gram method}, {Gram's procedure}, {Gram's stain}]