ret‧ro‧fit /ˈretrəʊfɪt $ -troʊ-/ verb (past tense and past participle retrofitted, present participle retrofitting) [transitive]
to improve a machine, piece of equipment, building etc by putting new and better parts in it after it has been used for some time:
plans to retrofit oil boilers
—retrofit noun [countable]
—retrofitting noun [uncountable]

[TahlilGaran] Dictionary of Contemporary English ▲