confidence

1. Trust or faith in a person or thing.

2. A trusting relationship: I took them into my confidence.

3. 1. That which is confided; a secret: A friend does not betray confidences.

   2. A feeling of assurance that a confidant will keep a secret: I am telling you this in strict confidence.

4. A feeling of assurance, especially of self-assurance.

5. The state or quality of being certain: I have every confidence in your ability to succeed.

Synonyms: These nouns denote a feeling of emotional security resulting from faith in oneself. Confidence is a firm belief in one's powers, abilities, or capacities: "You gain strength, courage and confidence by every experience in which you really stop to look fear in the face" (Eleanor Roosevelt).
Assurance even more strongly stresses certainty and can suggest arrogance: How can you explain an abstruse theory with such assurance?
Aplomb implies calm poise: "It is native personality, and that alone, that endows a man to stand before presidents or generals . . . with aplomb" (Walt Whitman).
Self-confidence stresses trust in one's own self-sufficiency: "The most vital quality a soldier can possess is self-confidence" (George S. Patton).
Self-possession implies composure arising from control over one's own reactions: "In life courtesy and self-possession . . . are the sensible impressions of the free mind, for both arise . . . from never being swept away, whatever the emotion, into confusion or dullness" (William Butler Yeats). See Also Synonyms at trust.