pros·the·sis 
(prŏs-thēsĭs)
(prŏs-thēsĭs)n. pl. pros·the·ses (-sēz)
1. An artificial device used to replace a missing body part, such as a limb, tooth, eye, or heart valve.
2. Replacement of a missing body part with such a device.
3. Linguistics Prothesis.
[Greek, addition, from prostithenai, prosthe-, to add : pros-, pros- + tithenai, to put; see dhē- in the Appendix of Indo-European roots.]
prosthesisathlete wearing a prosthetic leg used for running