main β chief in size, extent, or importance; principal; leading: the company's main office; the main features of a plan.
basic β You use basic to describe things, activities, and principles that are very important or necessary, and on which others depend.
fundamental β serving as, or being an essential part of, a foundation or basis; basic; underlying: fundamental principles; the fundamental structure.
important β of much or great significance or consequence: an important event in world history.
key β a small metal instrument specially cut to fit into a lock and move its bolt.
paramount β chief in importance or impact; supreme; preeminent: a point of paramount significance.
pivotal β of, relating to, or serving as a pivot.
middle β equally distant from the extremes or outer limits; central: the middle point of a line; the middle singer in a trio.
midway β several U.S. islets in the N Pacific, about 1300 miles (2095 km) NW of Hawaii: Japanese defeated in a naval battle June, 1942; 2 sq. mi. (5 sq. km).
primary β first or highest in rank or importance; chief; principal: his primary goals in life.
prime β of the first importance; demanding the fullest consideration: a prime requisite.
radical β of or going to the root or origin; fundamental: a radical difference.
ruling β a principle or regulation governing conduct, action, procedure, arrangement, etc.: the rules of chess.
salient β prominent or conspicuous: salient traits.
umbilical β of, relating to, or characteristic of an umbilicus or umbilical cord.
axial β relating to, forming, or characteristic of an axis