(1) The source of an artist's inspiration
"Euterpe was his muse"
(2) In ancient Greek mythology any of 9 daughters of Zeus and Mnemosyne; protector of an art or science
(3) Reflect deeply on a subject
"I mulled over the events of the afternoon"
"Philosophers have speculated on the question of God for thousands of years"
"The scientist must stop to observe and start to excogitate"