Important, indispensable, crucial.

(set phrase) Time is an essential consideration (in regard to an action or response); haste is necessary.

(idiomatic) The best person or item in a group; the best that one has to offer.

(idiomatic) The part of town that is not inhabited by the wealthy. An area where the working class, poor or extremely poor live.

(idiomatic) The best or most desirable among some selection.

To walk, decomposed, to stress the fundamentality of the task. / (idiomatic) To move forward, progress steadily.

A judicial officer with varying responsibilities depending on the jurisdiction.

(idiomatic, almost always preceded by the, informal) The essential element (needed to reach the principal goal or objective); the overall purpose.

The quality of being middle-of-the-road.

Alternative spelling of middle of the road