noun

• An aside, an act of straying from the main subject in speech or writing.
• (generally uncountable) The act of straying from the main subject in speech or writing, (rhetoric) particularly for rhetorical effect.
• (obsolete) A deviancy, a sin or error, an act of straying from the path of righteousness or a general rule.
• (now rare) A deviation, an act of straying from a path.
• (astronomy, physics) An elongation, a deflection or deviation from a mean position or expected path.