Machine vs. engin
In French, both machine and engin can translate to machine or engine in English, but they are not interchangeable. Machine is a very general term, while engin is more specific, often referring to large, powerful, and mobile equipment.
Machine
A2This is the most common and general term for any device, apparatus, or appliance that uses mechanical or electrical power to perform a task. It can refer to anything from a simple household appliance to complex industrial equipment.
La machine à laver a fini son cycle.
(The washing machine has finished its cycle.)
J'ai besoin d'une nouvelle machine à café.
(I need a new coffee machine.)
Cette usine utilise une machine très complexe pour assembler les pièces.
(This factory uses a very complex machine to assemble the parts.)
Mon ordinateur est une machine puissante pour le montage vidéo.
(My computer is a powerful machine for video editing.)
Le corps humain est une machine incroyablement sophistiquée.
(The human body is an incredibly sophisticated machine.)
Il a acheté une boisson à la machine distributrice.
(He bought a drink from the vending machine.)
Engin
B1This word typically refers to a large, often self-propelled piece of equipment built for a specific, heavy-duty purpose. It is commonly used for vehicles in construction, agriculture, military, or aerospace contexts. It can also mean device or contraption, sometimes with a connotation of being dangerous, mysterious, or complex.
Un engin de chantier bloque la circulation.
(A piece of construction equipment is blocking traffic.)
Les pompiers ont utilisé un engin spécial pour atteindre le dernier étage.
(The firefighters used a special vehicle to reach the top floor.)
L'engin spatial se prépare pour le décollage.
(The spacecraft is preparing for takeoff.)
La police a découvert un engin explosif dans le colis.
(The police discovered an explosive device in the package.)
Il a inventé un étrange engin volant dans son garage.
(He invented a strange flying contraption in his garage.)
Les jet-skis sont des engins de plage très populaires.
(Jet skis are very popular watercraft.)
Summary
In essence, use machine as the default, general term for almost any device that performs a task, especially household appliances and computers. Use engin for large, powerful, mobile equipment like bulldozers, spacecraft, or military vehicles. Engin can also be used for a specific device, often one that is explosive or a strange contraption. You would never call your coffee maker an engin, but you could call a tractor a machine (though engin agricole is more precise).