there was also a time when an inverter was also an electromechanical device with a motor sharing a common shaft with a generator (for high voltage DC output) or an alternator (for AC output). the other names for these inverters were "denemotor", "motor-generator" (abbreviated MG in schematics), or "rotary inverter". such devices are still in use for very large applications. a few years back i worked for an AM radio station, and their transmitter was located in an area where 3-phase AC power was not available. there was a large (about 6ft long, and 3ft diameter) rotary inverter to convert single-phase AC to 3-phase for the transmitter. so the term "inverter" actually covers a wide range of devices. so the term broadly means "a device for converting a convenient simple source of power into a needed and normally unavailable source of power" in the early days of radio, it was common to use a huge rotary inverter to convert 110VDC to the 20-30khz RF power feeding almost directly into the antenna. these devices were called Alexanderson Alternators.