tuning key

noun

a device that may be placed over a wrest pin on a piano, etc, and turned to alter the tension and pitch of a string

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Examples from the Web for tuning key

Historical Examples of tuning key

But Czipra began to put the strings of the czimbalom out of tune with her tuning-key.
Debts of Honor
Maurus Jkai
"That I could help," said Arnold, as he took his tuning-key out of his pocket.
Atlantic Monthly, Vol. XII. July, 1863, No. LXIX.
Various
They had strings of brass wire which were tuned by a key, not very different from the present tuning-key.
The Story of Ancient Irish Civilization
P. W. Joyce