1. An enduring disposition or tendency of an organism to act in an organized and biologically adaptive manner characteristic of its species.
2. The unreasoning impulse to perform some purposeful action without an immediate consciousness of the end to which that action may lead.
3. In psychoanalytic theory, the forces or drives assumed to exist behind the tension caused by the needs of the id.
The information shown above for instinct is provided by Stedman's.
* Stedman's, part of Lippincott Williams & Wilkins, provide a comprehensive line of health-science publications for healthcare professionals and medical students.