A monophonic synthesizer or monosynth is a synthesizer

Synthesizer

A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...

 that produces only one note at a time, making it smaller and cheaper than a polysynth, a synthesizer which can play multiple notes at once; most later synthesizers are polysynths.

Well-known monosynths include the Minimoog

Minimoog

The Minimoog is a monophonic analog synthesizer, invented by Bill Hemsath and Robert Moog. It was released in 1970 by R.A. Moog Inc. , and production was stopped in 1981. It was re-designed by Robert Moog in 2002 and released as Minimoog Voyager.The Minimoog was designed in response to the use of...

, Roland SH-09 and the Korg Prophecy

Korg Prophecy

The Korg Prophecy is considered one of the earliest "virtual analog" synthesizers, although its synthesis capabilities went beyond many of its VA contemporaries....

.

Electropop group Joy Electric

Joy Electric

Joy Electric is the brand label for a series of electropop/synth pop productions by Ronnie Martin. Martin began producing music under the Joy Electric name in 1994, after the demise of Dance House Children, a band Ronnie was in with his brother Jason Martin of Starflyer 59. Starflyer 59 bass player...

 released a song entitled "Monosynth" on their album Robot Rock

Robot Rock

Robot Rock is the third full-length album by Joy Electric. In 2006, it was rereleased on iTunes, along with Melody & CHRISTIANsongs. This was the first Joy Electric album that almost completely left the fairy-tale theme and took on a more "punk rock" attitude...

.