It's found in many English words, like:
* Audio: Relating to sound.
* Audience: A group of people gathered to hear something.
* Auditory: Relating to the sense of hearing.
* Audible: Capable of being heard.
* Auditorium: A large hall for public gatherings, especially for concerts or lectures.
* Audacious: Bold and daring, literally "to be bold enough to hear" (referring to a challenge).
This root word's meaning is reflected in its usage in many different contexts.