audeo

Audeo, audere, ausus sum is semi-deponent, which is the whole point of the word. The present system is ordinary second conjugation active, audeo, audes, audet, audebam; the perfect system is passive in form and active in meaning, ausus sum, ausus eram. There are only four common verbs like this: audeo, gaudeo, soleo and fido. Learn them as a set and the pattern stops being a surprise.

So ausus est is "he dared", never "he was dared". It usually takes a plain infinitive. The related adjective audax, audacis, "bold", slides towards "reckless" when a Roman writer wants to disapprove, and audacia is nerve of the wrong sort as often as of the right. English audacity, audacious and, at a distance, the French oser all come from here. Do not confuse audeo with audio, "I hear".