Alternative form of A1

Alternative spelling of A1

(US, military, historical) Cox-Klemin A-1 Air Ambulance, never mass produced. / (US, military) Skyraider single engine general-purpose attack aircraft.

Alternative form of one-on-one

(Internet slang) Used to signify agreement with the comment to which one is replying.

To a high degree.

A selective service class denoting that the registrant is available for service in the military

(US, colloquial) First class, superior.

(sports, skateboarding, snowboarding, skiing) Clipping of 180. (180° spin)

The number one (1). / (Internet slang, leetspeak, sarcastic) Deliberate misspelling of !, imitating someone who is too excited to consistently press the shift key while typing exclamation marks.