A necessary ingredient.
A fundamental ingredient.
Necessary.
Necessary for survival but not synthesized by the organism, thus needing to be ingested.
Being in the basic form; showing its essence.
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.
Not any thing; no thing.
An absence of anything, including empty space, brightness, darkness, matter, or a vacuum.
Something trifling, or of no consequence or importance.
A trivial remark especially in the term sweet nothings.
A nobody (insignificant person).