The term GREEK D is represented by the crossword solution DELTA, which is a five-letter word. DELTA is the fourth letter of the Greek alphabet and is often used to represent change or difference in mathematics, science, and engineering. It is also used to refer to the triangular shape formed by the intersection of two lines, or the area enclosed by a river's branches. In addition, it is a symbol of the Greek goddess Demeter and is associated with the ancient Greek city-state of Sparta.