1
general::
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]
American Heritage Idioms
2
general::
Phrase(s): tickle the ivories
to play the piano. • I used to be able to tickle the ivories real nice. • She sat down to tickle the ivories for a while.
McGrawhill's American Idioms And Phrasal Verbs