In China there is an instrument called a yángqín, now written 揚琴, that is "exalted zither." It sounds like this.

The word "yángqín" was, by all accounts, originally written 洋琴: "foreign [particularly, Western] zither." This is assumed to denote its origins in the barbarian wilds. Wikipedia offers a number of possible precursors and routes of ingress, from Iranian santurs hauled up the Silk Road to Portuguese salterios shipped into China's port cities only a few hundred years ago. (And, of course, the inevitable theories of intrasinitic origin, although I see no real reason to believe these.)

Since then, the name changes that the yángqín has gone through are a bit complicated. Wikipedia claims that the characters used to write "yángqín" were only changed to 揚琴 in 1910, but offers no source for this assertion, and I happen to know that:

1. The word 楊琴 ("willow zither": same pronunciation, different first character) was used in Japan in the 1800s (and possibly earlier) to refer to a kind of Chinese zither used by certain street musicians (not the yángqín being discussed here)
2. Assuming that the original was 洋琴, 楊琴 and 揚琴 are exactly the sort of variant, sound-derived orthographies that would get confused in the days before spellcheck.

The most likely-seeming sequence of events that I can reconstruct is that the original name, 洋琴, was corrupted based on sound and folk etymology into first one and then the other of 楊琴 and 揚琴, resulting in a situation where all three coexisted (and were applied to a variety of more or less related instruments) until whatever defining event in 1910 Wikipedia is referring to.

Meanwhile, in Japan, there are still some sources and institutions in Japan who prefer 洋琴　for the yángqín — the Kōjien dictionary, for example — but in general the characters 洋琴 are deprecated for the yángqín. They have been commandeered for the piano instead, you see. (Or, more rarely, the pipe organ, although 風琴, literally "wind zither," is more common in that case.)

Most of the instances of "洋琴" on Aozora Bunko are piano or organ references:

• ある秋仏蘭西（フランス）から来た年若い洋琴家（ピアニスト）が = "One autumn, a young pianist from France..." (Kajii Motojirō 梶井基次郎, "Kigakuteki genkaku" 器楽的幻覚, "An instrumental vision")
• ああ、こんなじゃ洋琴（オルガン）も役に立たない = "Ugh, at this rate even an organ wouldn't do any good" (Izumi Kyōka 泉鏡花, "Chikai no maki" 誓之巻, "Scroll of vows")
• 円い磨硝子（すりがらす）の笠をかけた朦朧（もうろう）たるランプの火影に、十九歳のロザリンが洋琴（ピアノ）を弾きながら低唱したあのロマンス = "The romance of nineteen-year-old Rosalyn in the dim light of the lamp with its ground-glass lampshade, singing softly as she played the piano" (Nagai Kafū 永井荷風, "Kaiyō no tabi" 海洋の旅, "A voyage by sea")

(Note too that these are written 洋琴, but with instructions to pronounce them piano or orugan rather than yōkin, the Japanese version of yángqín. The good old days.)

Poor old yángqín. One century it's so Western it gets called the "Western zither"; the next century it's not even Western enough to deserve the name.