(idiomatic) First; foremost; best, often used after its headword.

The most important person, the one who is in charge. / Someone who is top of a ranking, who is ranked first. / Oneself, being considered foremost, as by an egoist.

Alternative form of all as one

(idiomatic) Attentive, active, busy or alert.

(US, colloquial) murder in the first degree.

In a situation which is entirely suitable, familiar, or enjoyable.

The very beginning. / (US, slang) A close, longtime friend, one who has been around since the beginning.

At the very beginning; when something is entirely new.

(soccer) A quick one-touch play between two players. / (boxing) A one-two punch; two punches delivered in rapid succession / Two things in short succession

The highest class of motor racing sanctioned by the FIA.