(n)key, paint(basketball) a space (including the foul line) in front of the basket at each end of a basketball court; usually painted a different color from the rest of the court“he hit a jump shot from the top of the key”, “he dominates play in the paint”
(s)cardinal, central, fundamental, key, primalserving as an essential component“a cardinal rule”, “the central cause of the problem”, “an example that was fundamental to the argument”, “computers are fundamental to modern industrial structure”