The term PETRI DISH MEDIUM is a combination of two words. The first word, Petri Dish, is a shallow cylindrical glass or plastic lidded dish that is used to culture cells and bacteria. The second word, Medium, refers to the nutrient-rich substance in which the cells and bacteria are grown. The crossword solution for this term is AGAR, which is a gelatinous substance derived from seaweed that is used as a growth medium for microorganisms.