Definition of "Retrofit" :
noun: the act of adding a component or accessory to something that did not have it when it was manufactured
"The court ordered a retrofit on all automobiles."
noun: a component or accessory added to something after it has been manufactured
verb: substitute new or modernized parts or equipment for older ones
"The laboratory retrofitted to meet the safety codes."
verb: fit in or on an existing structure, such as an older house
"The mansion was retrofitted with modern plumbing."
verb: provide with parts, devices, or equipment not available or in use at the time of the original manufacture
"They car companies retrofitted all the old models with new carburetors."