From milli-, meaning one thousanth and Helen, the name of a beautiful woman from classic literature.
Unit for measuring beauty. One millihelen is the ammount of beauty that will launch exactly one ship.
Backround information: In the epic poem "The Illiad" by Homer, Helen of Troy is considered the most beautiful woman. Her beauty was the cause the Trojan war, because a man named Paris declaired her the most beautiful, and not one of the godesses. Because her beauty caused many men to go to war (in a society that revolved around the sea and boats), it can be said that her face was so beautiful it launched one thousand ships. So, one milli-Helen would be one thousanth of a Helen, or enough to launch one ship.
Alternate spelling: millihelen
This word was used by the character Zane in Scott Westerfeld's novel "Pretties":
Zane: "What would you give the view?"
Tally: "Give it?"
Zane: "A hundren milli-Helens? Five hundred? Maybe a whole Helen?"
Tally: "I'd give it none. It's Uglyville, after all."