Essential
Part of speech: adjective
Definition: Necessary. Very important; of high importance. Being in the basic form; showing its essence. 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.
Part of speech: noun
Definition: A necessary ingredient. A fundamental ingredient.
Example sentence: Half an hour's meditation each day is essential, except when you are busy. Then a full hour is needed.
Crucial
Part of speech: adjective
Definition: Being essential or decisive for determining the outcome or future of something; extremely important.Cruciform or cruciate; cross-shaped.Term of approval, particularly when applied to reggae music.
Example sentence: What is crucial in dealing with loss is not to lose the lesson. That makes you a winner in the most profound sense.