Hi Fiddler2007,

There is not a definitive reason why the Harmonica is commonly referred to as a Harp.

However here are a few snippets from my browsing on the subject:

The name "harp" is not a replacement for "harmonica."

The instrument was called a harp before it was called a harmonica.

And harmonica was already the name of another instrument.

The first harmonicas were called Aeolina - which refers to a harp
whose strings are excited to sound by wind. Here the reeds replace
strings. Other early harmonicas were called "mundharfe" - mouth-harp.
I'm not sure when the harmonica name was first borrowed to refer to
our instrument.

Meanwhile, the name "harmonica" referred to at least one other
instrument, the most recent of which was the glass harmonica, which
operated by the friction of the fingers against wet glass. Benjamin
Franklin is said to have invented a form of this instrument that
resembled a treadle-operated lathe, with several glass discs of
different sizes (and pitches) rotating in a trough of water.

Mouth organ is perhaps the most technically accurate, as free reeds
are also used in organs and harmoniums.

Best Regards
Nigel

Nigel Spiers
Christchurch, New Zealand
info@nzacoustics.com