1) forming, of, the main, most important or useful part (basic)

2) the nature or most important quality (of something) (essence)

3) necessary; most important (essential)

4) the side nearer or towards or more often seen; most important side (front)

5) the belief that pleasure is the most important thing in life (hedonism)

6) chief; most important (leading)

7) chief; most important (main)

8) the most important or chief kind, tendency etc (mainstream)

9) most important or most significant; easily noticed (salient)

10) (a particular kind of) matter; the most important part; chief or real meaning of something (substance)