ETYM Pref. a- + side.
1. In reserve; not for immediate use; SYN. by, away.
2. On or to one side.
3. Out of the way (especially away from one's thoughts); SYN. away.
4. Placed or kept separate and distinct as for a purpose; SYN. apart.

A line spoken by an actor to the audience but not intended for others on the stage.
Words in a play spoken to the audience alone, conventionally unheard by the other characters on stage. For example: Cordelia (aside): “What shall Cordelia speak?” Many other characters in Shakespeare’s King Lear are on stage, but the aside is intended for the audience alone to understand her feelings.

Beyond, past