essential

es·sen·tial

adj \i-ˈsen-chəl\

Definition of ESSENTIAL

1

: being, relating to, or containing an essence <an essential odor>

2

: being a substance that is not synthesized by the body in a quantity sufficient for normal health and growth and that must be obtained from the diet <essential fatty acids>—compare nonessential

3

: having no obvious or known cause : idiopathic <essential disease>