Papanicolaou (Pap) stain

Pa·pa·ni·co·laou (Pap) stain

(pap'ă-ni'kō-low pap stān) A multichromatic stain used principally on exfoliated cytologic specimens and based on aqueous hematoxylin with multiple counterstaining dyes in 95% ethyl alcohol, giving great transparency and delicacy of detail; important in cancer screening, especially of gynecologic smears.