trypan blue Syllabification: (try·pan blue)Pronunciation: /ˈtripən, trəˈpan/Definition of trypan blue noun a diazo dye used as a biological stain due to its absorption by macrophages of the reticuloendothelial system. Origin: early 20th century: trypan from trypanosometrypan blue in other Oxford dictionaries Definition of trypan blue in the British & World English dictionary