Final answer:
The combining form audi(o) is closest in definition to hearing.
Step-by-step explanation:
The combining form audi(o) is closest in definition to hearing. Hearing, also known as audition, is the transduction of sound waves into a neural signal that is made possible by the structures of the ear. These structures include the external ear, which consists of the auricle, auditory canal, and eardrum, as well as the middle ear, which contains three small bones called the ossicles. Finally, the sound waves are transduced into a neural signal in the inner ear.