Ahimsa
अहिंसा (ahiṃsā)
Non-harm - the first restraint of yoga, extending from action to speech to the tone of one's own thoughts.
Ahimsa - literally the absence of himsa, injury - stands first among the yamas, the restraints that open Patanjali's path, and first in Jain ethics, which developed it furthest. Its position is the point: whatever else practice builds must rest on not adding harm.
Its reach is wider than violence. Speech harms; haste harms; the tone one takes with one's own failures harms, and that inner harshness reliably leaks outward. Gandhi's political ahimsa was an application of something originally more intimate.
Practised honestly, ahimsa is not the absence of force but the presence of care. Some days it means saying the hard thing gently; some days it means saying nothing; occasionally it means acting firmly so that a larger harm does not proceed. Discernment, again, is the hinge.