The audacious firefighter saved the two people in the burning building.
He was an audacious explorer.
He was audacious in his pursuit of the movie star.
Annabelle was so audacious that she called her teacher incompetent int he middle of class.
You could use it anywhere you would use "daring" or "reckless". for example: "He had an audacious plan to swim across the English Channel at night."
Audaciousness is the abstract noun form for the adjective audacious.
The audacious young man decided to climb the tallest mountain in the region with no prior experience.
The man replied rather AUDACIOUSLY. :D
Walking the tightrope between the two high buildings on a windy day was an audacious stunt.
Unrattled.....
Brazen
brazen
Audacious derives from the Latin word audax, meaning "brave, daring". When declined, this Latin adjective took the form audac-.Audacious has been in the English language since at least 1550. Audacity dates back to at least 1450.