What term is used to describe an instrument that aids or compensates for defective human hearing?

The term "hearing aid" specifically refers to a device designed to improve hearing by amplifying sound for individuals who have hearing loss. This makes it the most accurate choice when describing an instrument that compensates for defective hearing. Hearing aids are tailored to assist users by making sounds clearer and more audible, often including features that can be customized based on the user's specific type of hearing impairment.

While other options like "auditory device," "sound enhancer," and "audio amplifier" may relate to sound and hearing, they do not accurately define the specific function of assisting individuals with hearing loss in the same way that "hearing aid" does. An auditory device could encompass a broad range of technologies beyond just those meant for individuals with hearing deficiencies, and while a sound enhancer or audio amplifier could potentially assist in certain contexts, they are not exclusively or specifically designed for hearing impairment.