A person who formally examines and verifies financial accounts.

The *auditing* of a company's financial records by independent examiners on a regular basis is necessary to prevent “cooking the books,” and thus to keep the company honest. We don't normally think of auditors as listening, since looking at and adding up numbers is their basic line of work, but auditors do have to listen to people's explanations, and perhaps that's the historical link. Hearing is more obviously part of another meaning of *audit*, the kind that college students do when they sit in on a class without taking exams or receiving an official grade.

(1) Perceived or experienced through hearing. (2) Of or relating to the sense or organs of hearing.

*Auditory* is close in meaning to *acoustic* and *acoustical*, but *auditory* usually refers more to hearing than to sound. For instance, many dogs have great auditory (not acoustic) powers, and the *auditory nerve* lets us hear by connecting the inner ear to the brain. *Acoustic* and *acoustical* instead refer especially to instruments and the conditions under which sound can be heard; so architects concern themselves with the acoustic properties of an auditorium, and instrument makers with those of a clarinet or piano.

A trial performance to evaluate a performer's skills.

Most stars are discovered at auditions, where a number of candidates read the same part and the director chooses. Lana Turner famously skipped the audition process and was instead discovered by an agent sipping a soda in a Sunset Boulevard café at age 16. *Audition* can also be a verb; so, for example, after Miss Turner gained her stardom, actors had to audition to be her leading man. But when musicians audition for a job in an orchestra, it's usually behind a screen so that the judges won't even know their sex and therefore can't do anything but listen.

Not heard or capable of being heard.

With its negative prefix *in-*, *inaudible* means the opposite of *audible*. What's clearly audible to you may be inaudible to your elderly grandfather. Modern spy technology can turn inaudible conversations into audible ones with the use of high-powered directional microphones, so if you think you're being spied on, make sure there's a lot of other noise around you. And if you don't want everyone around you to know you're bored, keep your sighs inaudible.

(1) Having to do with sound. (2) Having to do with the speed of sound in air (about 750 miles per hour).

A sonic boom is an explosive sound created by a shock wave formed at the nose of an aircraft. In 1947 a plane piloted by Chuck Yeager burst the “sound barrier” and created the first sonic boom. In the decades afterward sonic booms became a familiar sound to Americans. (Because of steps that were eventually taken, sonic booms are rarely heard anymore.) Today *sonic* is often used by ambitious rock musicians to describe their experimental sounds.

(1) Clashing or discordant, especially in music. (2) Incompatible or disagreeing.

Since *dissonant* includes the negative prefix *dis-,* what is dissonant sounds or feels unresolved, unharmonic, and clashing. Early in the 20th century, composers such as Arnold Schoenberg and his students developed the use of *dissonance* in music as a style in itself. But to many listeners, the sounds in such music are still unbearable, and most continue to prefer music based on traditional tonality. *Dissonant* is now often used without referring to sound at all. *Cognitive dissonance*, for example, is what happens when you believe two different things that can't actually both be true.

(1) A continuing or echoing of sound. (2) A richness and variety in the depth and quality of sound.

Many of the finest musical instruments possess a high degree of resonance which, by producing additional vibrations and echoes of the original sound, enriches and amplifies it. Violins made by the Italian masters Stradivari and Guarneri possess a quality of resonance that later violinmakers have never precisely duplicated. And you may have noticed how a particular note will start something in a room buzzing, as one of the touching surfaces begins to *resonate* with the note. Because of that, *resonance* and *resonate*—along with the adjective *resonant*—aren't always used to describe sound. For example, you may say that a novel resonates strongly with you because the author seems to be describing your own experiences and feelings.

Having a frequency higher than what can be heard by the human ear.

*Ultrasound*, or *ultrasonography,* works on the principle that sound is reflected at different speeds by tissues or substances of different densities. Ultrasound technology has been used medically since the 1940s. *Sonograms,* the pictures produced by ultrasound, can reveal heart defects, tumors, and gallstones; since low-power ultrasonic waves don't present any risks to a body, they're most often used to display fetuses during pregnancy in order to make sure they're healthy. *Ultrasonics* has many other uses, including underwater *sonar* sensing. High-power ultrasonics are so intense that they're actually used for drilling and welding.