tickle the ivories
Play the piano, as in He went on tickling the ivories until three in the morning. This expression alludes to a piano's keys, traditionally made of ivory. [Colloquial; first half of 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.