audacity

1. Fearless daring; intrepidity.
2. Bold or insolent heedlessness of restraints, as of those imposed by prudence, propriety, or convention.
3. An act or instance of intrepidity or insolent heedlessness: warned the students than any audacities committed during the graduation ceremony would be punished.

noun

1. Willingness to take risks: adventuresomeness, adventurousness, audaciousness, boldness, daredevilry, daredeviltry, daring, daringness, venturesomeness, venturousness. See safety/danger.
2. The state or quality of being impudent or arrogantly self-confident: assumption, audaciousness, boldness, brashness, brazenness, cheek, cheekiness, chutzpah, discourtesy, disrespect, effrontery, face, familiarity, forwardness, gall, impertinence, impudence, impudency, incivility, insolence, nerve, nerviness, overconfidence, pertness, presumptuousness, pushiness, rudeness, sassiness, sauciness. Informal brass, crust, sauce, uppishness, uppityness. See attitude/good attitude/bad attitude/neutral attitude, courtesy/discourtesy.

Definition: arrogance, presumptuousness
Antonyms: gentility, humility, meekness, modesty, timidity, yielding

n

Definition: recklessness, daring
Antonyms: care, carefulness, caution, reserve, timidity

The noun has 2 meanings:

Meaning #1: fearless daring
  Synonyms: audaciousness, temerity

Meaning #2: aggressive boldness or unmitigated effrontery
  Synonyms: audaciousness, hutzpa, chutzpah