The term 'INGREDIENT IN SPANAKOPITA' can be solved by the four letter word 'FETA'. Feta is a type of cheese that is commonly used in Greek cuisine, particularly in dishes such as spanakopita. Spanakopita is a savory pastry made with phyllo dough and filled with a mixture of feta cheese, spinach, onions, and herbs. Feta is an essential ingredient in this dish, providing a salty, tangy flavor that complements the other ingredients.