Which word describes the quality of having great self-assurance?

The term "aplomb" refers to a state of self-assurance, confidence, and composure, particularly in demanding situations. It embodies the idea of being poised and maintaining confidence irrespective of external pressures. This quality is often associated with someone who can navigate challenges with ease and certainty, exhibiting a calm and collected demeanor.

In contrast, other words in the question refer to different qualities. Hesitation indicates uncertainty or reluctance to act, timidity describes a lack of confidence or courage, and desperation implies a state of extreme need or urgency, often accompanied by anxiety or fear. None of these alternatives convey the positive connotation associated with having great self-assurance that "aplomb" does.