Prosthesis: noun. New Latin prothesi(n), from Greek próthesis, addition, from prostithenai to add to, from pros- in addition to + tithenai to place.

1 ( med.) Replacement of a missing or impaired body part with an artificial device to recover its functionality; can be defined prostheses aswell external devices meant to improve the function of a body part without replacing it: for example Auditory Prosthesis, generic term for implantable devices to restore sound perception to people with profound hearing impairment or deafness, the most common of which is the cochlear implant. These devices substitute the functions performed by the ear drum and stapes with a microphone, while an external unit gathers the sound and processes it, simulating the frequency analysis performed in the cochlea.

2 (metaph.) Any artificial element replacing the natural one.