PRIMARY

A primary election; a preliminary election to select a political candidate of a political party.

The first year of grade school.

A base or fundamental component; something that is irreducible.

To challenge (an incumbent sitting politician) for their political party's endorsement to run for re-election, through running a challenger campaign in a primary election, especially one that is more ideologically extreme.

To take part in a primary election.

First or earliest in a group or series.

"Children attend primary school, and teenagers attend secondary school."

Main; principal; chief; placed ahead of others.

"Preferred stock has primary claim on dividends, ahead of common stock."

Earliest formed; fundamental.