(adverb)
into privacy, so as not to be seen or heard by others;
e.g. You should take her aside and tell her why what she said was wrong.
(adverb)
away in reserve, especially so as to be available for use in the future;
e.g. It is wise to keep some money aside to be used in case of emergencies.
(noun)
a remark or speech made by an actor in a play that is meant to be heard by the audience but not by the characters in the play, or broadly, a remark that is not meant to be heard by other people;
e.g. The actor made an aside to the audience, causing them to laugh.
(noun)
a remark or discussion that is not directly relevant or related to the main topic;
e.g. They ignored his aside because they were on a tight schedule.