WordNet (r) 3.0 (2006):

Gram stain
    n 1: 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, Gram
         stain]