Being in the basic form; showing its essence.
Necessary.
Necessary for survival but not synthesized by the organism, thus needing to be ingested.
Really existing; existent.
Very important; of high importance.
Having the nature of essence; not physical.
Such that each complementary region is irreducible, the boundary of each complementary region is incompressible by disks and monogons in the complementary region, and no leaf is a sphere or a torus bounding a solid torus in the manifold.
Idiopathic.
A necessary ingredient.
A fundamental ingredient.
That operates to produce an effect.
Any of a class of behaviors that produce consequences by operating (i.e., acting) upon the environment.
An operative person or thing.