Nidana

The Causative factor
Nidana is the disease-causing factor. Diet, lifestyle or external factors like environmental variations (excessive heat, cold or rain), injuries or any other factors that disturb the doshas are considerednidana. If we know that certain foods or particular activities aggravate a dosha, we can avoid those causative and triggering factors and prevent manifestation or recurrence of disease.

In Ayurveda, nidana parivarjana or “avoiding the cause” is considered as the first line of treatment in most of the diseases. For example, avoiding heavy, sweet foodstuffs and sedentary lifestyle is the first step towards healing diabetes.

Cause; similar to Western term etiology; understanding the causitive factors of a condition.

Source: http://www.jiva.com/ayurveda/about-ayurveda/110.html