First or earliest in a group or series.
Main; principal; chief; placed ahead of others.
Earliest formed; fundamental.
Illustrating, possessing, or characterized by, some quality or property in the first degree; having undergone the first stage of substitution or replacement.
Relating to the place where a disorder or disease started to occur.
Relating to day-to-day care provided by health professionals such as nurses, general practitioners, dentists etc.

A primary election; a preliminary election to select a political candidate of a political party, or the first round of a two-round election.
The first year of grade school.
A base or fundamental component; something that is irreducible.
The most massive component of a gravitationally bound system, such as a planet in relation to its satellites.
A primary school.
Any flight feather attached to the manus (hand) of a bird.
A primary colour.
The first stage of a thermonuclear weapon, which sets off a fission explosion to help trigger a fusion reaction in the weapon's secondary stage.
A radar return from an aircraft (or other object) produced solely by the reflection of the radar beam from the aircraft's skin, without additional information from the aircraft's transponder.
The primary site of a disease; the original location or source of the disease.
A directly driven inductive coil, as in a transformer or induction motor that is magnetically coupled to a secondary.

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