(with appreciation to Wikipedia)
Ahimsa (Sanskrit: अहिंसा; IAST: ahimsā, Pāli: avihiṃsā) means 'not to injure' and refers to a key virtue in Indian religions. The word is derived from the Sanskrit root hiṃs – to strike; hiṃsā is injury or harm, a-hiṃsā is the opposite of this, i.e. cause no injury, do no harm. Ahimsa is also referred to as nonviolence, and it applies to all living beings—including all animals—in ancient Indian religions.
Ahimsa is one of the cardinal virtues and an important tenet of Jainism, Hinduism, and Buddhism. Ahimsa is a multidimensional concept, inspired by the premise that all living beings have the spark of the divine spiritual energy; therefore, to hurt another being is to hurt oneself. Ahimsa has also been related to the notion that any violence has karmic consequences. While ancient scholars of Hinduism pioneered and over time perfected the principles of Ahimsa, the concept reached an extraordinary status in the ethical philosophy of Jainism. Most popularly, Mahatma Gandhi strongly believed in the principle of ahimsa.
Ahimsa's precept of 'cause no injury' includes one's deeds, words, and thoughts. Classical literature of Hinduism such as Mahabharata and Ramayana, as well as modern scholars debate principles of Ahimsa when one is faced with war and situations requiring self-defence. The historic literature from India and modern discussions have contributed to theories of Just War, and theories of appropriate self-defence.
The word Ahimsa—sometimes spelled as Ahinsa—is derived from the Sanskrit root hiṃs – to strike; hiṃsā is injury or harm, a-hiṃsā is the opposite of this, i.e. non harming or nonviolence.
There is a debate on the origins of the word Ahimsa, and how its meaning evolved. Mayrhofer as well as Dumot suggest the root word may be han which means kill, which leads to the interpretation that ahimsa means do not kill. Schmidt as well as Bodewitz explain the proper root word is hiṃs and the Sanskrit verb hinasti, which leads to the interpretation ahimsa means do not injure, or do not hurt. Wackernagel-Debrunner concur with the latter explanation.
Ancient texts use ahimsa to mean non-injury, a broader concept than non-violence. Non-injury implies not killing others, as well as not hurting others mentally or verbally; it includes avoiding all violent means—including physical violence—anything that injures others. In classical Sanskrit literature of Hinduism, another word Adrohi is sometimes used instead of Ahimsa, as one of the cardinal virtues necessary for moral life. One example is in Baudhayana Dharmasutra 2.6.23: वाङ्-मनः-कर्म-दण्डैर् भूतानाम् अद्रोही (One who does not injure others with words, thoughts or acts is named Adrohi).
Ahimsa is imperative for practitioners of Patañjali's eight limb Raja yoga system. It is included in the first limb and is the first of five Yamas (self restraints) which, together with the second limb, make up the code of ethical conduct in Yoga philosophy. Ahimsa is also one of the ten Yamas in Hatha Yoga according to verse 1.1.17 of its classic manual Hatha Yoga Pradipika. The significance of Ahimsa as the very first restraint in the very first limb of Yoga (Yamas), is that it defines the necessary foundation for progress through Yoga. It is a precursor to Asana, implying that success in Yogasana can be had only if the self is purified in thought, word and deed through the self-restraint of Ahimsa.