Satya
Truthfulness.

Outer level: Being honest and forthright in one's actions, speech and also within oneself on the mind level. Not exaggerating or lying. Avoiding deceiving others or oneself. Lack of manipulativeness. Working honestly and pursuing right livelihood--that which reflects and encourages one's values.
Inner level:
Having greater freedom as the result of taking greater responsiblity to live truthfully on all levels. Trust in oneself. Trust in one's own discernment and ability to make decisions. Greater appreciation and tolerance for whatever life brings us drawn from not taking refuge in half-truths and seeing things more clearly for what they are.
Secret level: "When the practitioner is established in truthfulness, whatever is said by that person comes to fruition." Yoga Sutra II.36, Sadhana Pada

Further commentary is forthcoming...!

See also
Ahimsa, Asteya, Brahmacharya, Aparigraha