The term 'NADIR's Opposite' can be answered with four different crossword solutions: ZENITH (6 letters), ACME (4 letters), APOGEE (6 letters), and APEX (4 letters). ZENITH is the highest point in the sky, directly opposite of the NADIR, which is the lowest point in the sky. ACME is the highest point or peak of a development, while APOGEE is the farthest point from the Earth in an orbit around it. Lastly, APEX is the highest point of something, such as a mountain.