Gound (pronounced "gowned")
We also learned another of its nicknames: optiboogers. And we agreed that Optiboogers would be an excellent name for a rock band. Also Gingerbread Godzilla. And Giant Pez Dispenser. Stay tuned for gingerbread Godzilla, whom we all decided should make an appearance this Christmas.
Anyway, gound is composed of mucus, tears, and/or dust, and it forms because you're not blinking those things away when you're asleep.
What is your family's word for gound?