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Wikipedia says that a ciaccona (chaconne) is a musical composition involving variations on a harmonic progression or melody (motif), similar to the passacaglia. Both originated from Spain in the baroque era. Both have a basso ostinato. Both are (often) written in triple meter.

Another quote from Wikipedia:

The two genres are closely related, but since "composers often used the terms chaconne and passacaglia indiscriminately [...] modern attempts to arrive at a clear distinction are arbitrary and historically unfounded". [Bukofzer 1947, 42.] In early scholarship, attempts to formally differentiate between the historical chaconne and passacaglia were made, but researchers often came to opposite conclusions.

So, what is the difference between a ciaccona and a passacaglia? That quoted statement is from 1947, I assume that musicologists must have figured it out by now?

And here is a related question: What is the motif used in many chaconnes in the 17th century?

Both terms have come to be interchangeable. Chaconne from Spain, and passacaglia from either Spain or Italy. Both in slow three time, and both apparently using a ground bass. Danced to in France into the early 18th C. So mixed up that in Gluck's opera 'Paris and Helen', it was called a 'chiacone', but the same piece in 'Iphigenia in Aulis' it became a 'passecaille'.

So, to all intents and purposes, if you're writing one, and aren't sure what to call it - toss a coin!

"The greatest of the dance tunes is probably the Ciacona, Chaconne, with her brother, or her sister, the Passagaglio, or Passecaille. "

(Johann Mattheson: The Perfect Kapellmeister 1739, p. 233.)

In the musicology of the 20th and 21st centuries, much has been written or speculated about the difference between Ciaccona and Passacaglia, or Chaconne and Passacaille. As in the above formulation by Mattheson, it is "sister genres" that are sometimes difficult to differentiate, at least on paper, and are often treated in the same breath by the composers themselves and contemporary Baroque music theorists.

Passacaglia or Passagaglio [ital.], Passacaille [gall.], Is actually a chaconne. The whole difference is that it is ordinarily slower than the chaconne, the melody is milder, and expression is not so vivid; and that's why the Passecaillen are almost always in the modes minoribus, d. i. set in such tones that have a soft third.“

( Johann Walther: Johann Walther, Musical Lexicon, Leipzig 1732.)

According to this, the Passacaglia, in contrast to the Chaconne, is characterized by a softer, sweeter or more melancholy character, and therefore appears more often than this (but not always!) In minor.

Mattheson confirms this tonal tendency in his Perfect Kapellmeister in 1739

Source:

https://de.wikipedia.org/wiki/Chaconne

There seems to be no consensus among theorist about the tempi (Rameau, Rouseau).

Frescobaldi, who was probably the first composer to treat the chaconne and passacaglia comparatively, usually (but not always) sets the former in major key, with two compound triple-beat groups per variation, giving his chaconne a more propulsive forward motion than his passacaglia, which usually has four simple triple-beat groups per variation.[10] Both are usually in triple meter, begin on the second beat of the bar, and have a theme of four measures (or a close multiple thereof). (In more recent times the chaconne, like the passacaglia, need not be in 3
4 time; see, for instance, Francesco Tristano Schlimé's Chaconne/Ground Bass, where every section is built on seven-beats patterns)

https://en.wikipedia.org/wiki/Chaconne

The German wiki site is about 5 x more extensive than the English but there is so much detailed information that can‘t be summarized in a few words.