first (in order) / first (in time) / first (most important) / first (best in some regard)

(mathematics) prime

Denotes first day of the month first

(historical, politics) the First World

(idiomatic) any, every Tom, Dick and Harry (selected without thought as the most readily available at any given time)

(number theory) prime factor (a factor of a given integer which is also a prime number)

(military, idiomatic) First Lord of the Admiralty

(idiomatic) Alternative form of pierwszy lepszy

(idiomatic) at first glance, on the face of it (upon initial inspection)

(idiomatic) first come, first served