prosthesis

Concise Oxford English Dictionary © 2008 Oxford University Press:
prosthesis /prɒsˈθiːsɪs, ˈprɒsθɪˌsɪs/

▶noun (pl. prostheses /-siːz/)

• 1 an artificial body part.

• 2 the addition of a letter or syllable at the beginning of a word, as in Spanish escuela derived from Latin scola.

– derivatives
prosthetic /-ˈθɛtɪk/ adjective,
prosthetically adverb.

– origin C16: via late L. from Gk prosthesis, from prostithenai ‘add’.