I. ˈre.trō+ˌ-, sometimes ˈrē.trō+ˌ- noun
Etymology: retro- + fit
: a modification or addition of equipment (as on an aircraft or automobile) to include changes made in later production models
II. "ˌ transitive verb
Etymology: retrofit , noun
: to furnish (as a computer, airplane, or building) with new parts or equipment not available, considered necessary, or in place at the time of manufacture or construction