Wiktionary
archicembalo
n. (context musical instruments English) A form of harpsichord that had extra keys and strings
Wikipedia
Archicembalo
The archicembalo (or arcicembalo, ) was a musical instrument described by Nicola Vicentino in 1555. This was a harpsichord built with many extra keys and strings, enabling experimentation in microtonality and just intonation.