Machine , as here considered, is an assemblage of parts, movable and fixed, so constructed as to perform work when energy is applied to it. In size, a machine may vary from, e.g., a hand-operated numbering machine to a giant drop forge. Generally, a machine is thought of as more or less permanent and is expected to perform its work repeatedly or continuously over a long period of time.

Contrivance and device often mean a simply machine, sometimes improvised or makeshift, devised to perform a task once or for a short period of time. A belt attached to the rim of a drive wheel of a jacked-up car to power a circular saw is a contrivance or device .

A mechanism may be a simple machine or one of the moving system in a machine . A linotype machine includes a mechanism for spacing words evenly.

An apparatus is a complicated mechanism consisting of several separate but interconnected parts, usually constructed for a special purpose and not mass-produced. A chemist’s system of tubes and flasks is an apparatus constructed for a specific experiment or process.

An appliance , in current usage, is a household machine such as a washing machine , a vacuum cleaner, an electric mixer, etc. this notion of assisting in functions is also involved in appliances which help people to overcome physical disabilities; thus a hearing aid or a special aid of any kind worn on the body is an appliance .

An engine , properly speaking, is not a machine in the sense of something that performs a specific task; rather it is a machine that converts energy, as heat, electricity, water power, etc., into mechanical power: the steam engine ; the diesel engine .