the combination of components or elements to form a connected whole.Oxford Languages Dictionary
Synthesising a group of singers produces a choir; photosynthesising (synthesising light with) water and oxygen produces glucose and oxygen. Thus, in order for an electronic instrument to be considered a synthesiser, it must, in some manner, combine sonic elements.
In 1874, Elisha Gray invented the telephone near-simultaneously with Alexander graham Bell (though lost out on the attribution due to a late arrival at the patent office). To years later, as a byproduct, he also invented the “Musical Telegraph”: the first instrument to produce sound electronically. The musical telegraph is often referred to as the first synthesiser, however, this is not accurate. The instrument was capable only of producing single-tone oscillations and was not able to produce complex/composite wave-forms.
Electronic instruments were popularised around the turn 20th century, proceeding inventions such as the. The first “synthesiser” was created in the 50s. More and more virtual-instrument creators are turning towards physically-modelled synthesisers.