The premier of several musicians playing a particular instrument in an orchestra: seated closest to the audience, taking the lead for that instrument's movements, and playing any solos.

(idiomatic) second place.

A member of an emergency service who is first on the scene, or among those first on the scene, at an emergency. / A member of an emergency service trained to provide emergency medical care.

A country's most important city, usually the capital.

The leading woman in a specified field of endeavor. / Alternative spelling of First Lady

The wife of the chief executive of a nation; especially the wife of the President of a country; or a woman (e.g. a relative) who takes on similar public duties, as when the chief executive is unmarried.

(mathematics, logic) Of one of a series of models, languages, relationship, forms of logical discourse, etc., being the simplest one or the first in a sequence. / Of fundamental importance.

Happening for the first time; doing something for the first time.

(UK, military, nautical, historical) A first-rate ship of the line.

(UK, military, nautical, historical) Of a Royal Navy ship of the line in the Napoleonic Era: having at least 100 guns across three gun decks, a complement of 850–875, and weighing approximately 2,500 tons burthen.