The term Lucy comes from the song by the Beatles Lucy in the Sky with Diamonds which is commonly thought to be about LSD. Lucy is often used as a code word for LSD when referring to the drug in a public setting or over the phone where one does not want to openly discuss illegal activities. Lucy is used like a person's name in such discussions. Like saying Lucy took me on a trip last night to indicate you tripped on LSD the previous night. I tripped balls with Lucy last weekend!