essential

Necessary.

There’s canker at the root, your seed Denies the blessing of the sun, The light essential to your need. Your hopes are murdered and undone.

Thus, research-based resources with the potential to assist teachers prepare secondary students for tertiary education are essential.

Very important; of high importance.

In order to grant the rich these pleasures, the social contract is reconfigured. The welfare state is dismantled. Essential public services are cut so that the rich may pay less tax. […]

Necessary for survival but not synthesized by the organism, thus needing to be ingested.

Being in the basic form; showing its essence.

Don’t mind him being grumpy. That’s the essential Fred.

Really existing; existent.

Or is it true, that thou art but a bare name, / And no eſſential thing?

A necessary ingredient.

A fundamental ingredient.