Sentence:  In his teens O ' Banion was enrolled in the vicious Market Street gang and he became a <WSD>singing</WSD> waiter in McGovern's Cafe , a notoriously low and rowdy dive in North Clark Street , where befuddled customers were methodically looted of their money by the singing waiters before being thrown out . 
Meaning of the word marked with <WSD> tags:  the act of singing vocal music