In the genitive and attributive. Designating a stain or staining technique typically including methylene blue and eosin, used on blood smears and other types of smear and originally devised by Romanowsky for the demonstration of malaria parasites.
Late 19th century. From the name of Dmitrij Leonidovič Romanovskij, Russian physician, who described the staining technique in St. Petersburger medicinische Wochenschrift 16, no. 34 (24 Aug. 1891) 299.