If someone or something has primacy, they sit in first place — not always “the best” in a contest, but the one that comes first in rank, power, or importance. A country might claim primacy in a region; one idea might have primacy over another in a plan; a court might give primacy to one kind of right. It is a formal, almost official word: essays, law, church history, politics. You would not say it about a football match in the playground. Though actually, dictionaries sometimes gloss it as “best,” but speakers often mean “first in order or authority” rather than “most loved” or “highest quality.” Primacy can be given, taken, or fought over; it is about position. In older church talk it also named the rank of a primate, a chief bishop — same first-root, a narrower use.