CITHER
noun: cither 1. a musical stringed instrument with strings stretch over a flat sounding box; it is laid flat and played with a plectrum and with fingers [syn: zither, zithern] 2. a 16th century musical instrument resembling a guitar with a pear-shaped soundbox and wire strings
I knew it was one of the telegraph crosswords, but was not going to trawl through all of them to find out which one. They have put another post now with all the information.