The person or thing in the first position.

“He was the first to complete the course.”

The first gear of an engine.

Something that has never happened before; a new occurrence.

“This is a first. For once he has nothing to say.”

Preceding all others of a series or kind; the ordinal of one; earliest.

“I was the first runner to reach the finish line, and won the race.”

Most eminent or exalted; most excellent; chief; highest.

“Demosthenes was the first orator of Greece.”

Before anything else; firstly.

“Clean the sink first, before you even think of starting to cook.”

For the first time;

“I first witnessed a death when I was nine years old.”