adjective

• Self-generated; happening without any apparent external cause.
• Done by one's own free choice, or without planning.
• Proceeding from natural feeling or native tendency without external or conscious constraint.
• Arising from a momentary impulse.
• Controlled and directed internally; self-active; spontaneous movement characteristic of living things.
• Produced without being planted or without human cultivation or labor.
• Random.
• Sudden, without warning.