Misarticulation - inaccurately produced speech sound (phoneme) or sounds.

Noise Control System - a program used by manufacturers to control the amount of distracting extraneous noise that is transmitted to the hearing aid wearer.

Noise-Induced Hearing Loss - hearing loss caused by exposure to harmful sounds, either very loud impulse sound(s) or repeated exposure to sounds over 90-decibel level over an extended period of time that damage the sensitive structures of the inner ear.

Non- Programmable Hearing Aids - A type of hearing aid that is set for its sound levels at the manufacturer. Users must adjust the volume levels by hand using a small knob on the hearing aid. Some versions allow the user to adjust treble, mid range and  bass levels.

Nonsyndromic Hereditary Hearing Impairment - hearing loss or deafness that is inherited and is not associated with other inherited clinical characteristics.

Occulsion Effect - With certain hearing aid types - especially older models - this is the feeling that the ear is blocked up. It produces a distinctive "head in a barrel" feeling. More recent manufacturers have solved the problem by designing more open earpieces that allow the passage of air and pressure.
Ossicles -   Tthree tiny bones in the middle ear. They are known as the hammer, anvil and stirrups, or the  malleus, incus, and stapes. Their purpose is to deliver sound vibrations from the tympanic membrane to the cochlea in the inner ear.

Otitis Externa - inflammation of the outer part of the ear extending to the auditory canal.

Otitis Media - inflammation of the middle ear caused by infection.

Otoacoustic Emissions - low-intensity sounds produced by the inner ear that can be quickly measured with a sensitive microphone placed in the ear canal.

Otolaryngologist - physician/surgeon who specializes in diseases of the ears, nose, throat, and head and neck. Commonly known as an ENT - Ear Nose and Throat - doctor.

Otologist - physician/surgeon who specializes in diseases of the ear.

Otosclerosis - abnormal growth of bone of the inner ear. This bone prevents structures within the ear from working properly and causes hearing loss. For some people with otosclerosis, the hearing loss may become severe.

Outer Ear - The external, or visible portions of the ear.