According to Reference.com, "Macushla," or "Mo Chuisle" in Irish, literally means "my pulse." It is an Irish expression of affection originating in the late 19th century that means "darling" or "sweetheart." It is used in the phrase "a chuisle mo chroi," or "pulse of my heart."
"Macushla" is also the name of a 1910 Irish song with lyrics by Josephine V. Rowe and music by Dermot MacMurrough. "Macushla" was also used in the 1996 film "Michael Collins" during the end credits. In the film "Million Dollar Baby," it is inscribed on the boxing shorts of Hillary Swank's character and cheered by the crowd on numerous occasions.