retrofit

UK: /ˈrɛtrəʊˌfɪt/

US: /ˈrɛtroʊˌfɪt/

US: (v. re′trō fit′, re′trō fit′; n., adj. re′trō fit′)

Inflections of 'retrofit' (v): (⇒ conjugate)

retrofits

v 3rd person singular

retrofitting

v pres p

retrofitted

v past (US & UK)

retrofit

v past (US)

retrofitted

v past p (US & UK)

retrofit

v past p (US)

WordReference Random House Learner's Dictionary of American English © 2026

ret•ro•fit /ˈrɛtroʊˌfɪt,   v. [~ + object] , -fit•ted or -fit, -fit•ting. 

1. to supply (an automobile, airplane, etc.) with parts available after manufacture:
   to retrofit the old airplane with new cannons.

WordReference Random House Unabridged Dictionary of American English © 2026

ret•ro•fit  (v. re′trō fit′, re′trō fit′;n., adj. re′trō fit′), v., -fit•ted or -fit, -fit•ting, n., adj. 
v.t. 

1. to modify equipment (in airplanes, automobiles, a factory, etc.) that is already in service using parts developed or made available after the time of original manufacture.
2. to install, fit, or adapt (a device or system) for use with something older:
   to retrofit solar heating to a poorly insulated house.

v.i. 

3. (of new or modified parts, equipment, etc.) to fit into or onto existing equipment.
4. to replace existing parts, equipment, etc., with updated parts or systems.

n. 

5. something that has been retrofitted.
6. an instance of updating, enlarging, etc., with new or modified equipment:
   A retrofit could save thousands of dollars.

adj. 

7. being or characterized by a retrofit:
   retrofit units.

• retro- + fit¹

ret′ro•fit′ta•ble, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

retrofit / ˈrɛtrəʊˌfɪt/ verb ( -fits, -fitting, -fitted)

1. (transitive) to equip (a vehicle, piece of equipment, etc) with new parts, safety devices, etc, after manufacture