1) A popular girl's name.
2) A slang term to refer to
LSD (lysergic acid diethylamide). 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.