I love knowing the history of words and had to look this up.  It originated as luscus, a latin word for poor eyesight or blinded in one eye. In the early 19th century the French used the word to mean squinting, the way people shape their eyes to see better if they have poor eyesight.  They then gave it a figurative meaning also for people and things that are disreputable.  When the English adopted it use shortly after, they only used the second figurative meaning since they did not need the literal meanings.