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."