Yes, okay, no one will know what you're talking about if you use the word mumchance, but some words are just too gorgeous to leave on the shelf.
Really, using it will make the world a better place.
Mumchance means silent, or struck dumb. I think it can only be used of a person - I don't think you can have a mumchance forest (though even that might make a good title for a thriller) but the expression all I could do was sit mumchance will surely add lustre to any day.
A mumchance can mean also a silent, idle, and probably stupid person, too.
Mumchance has been both a dice and a card game. Unfortunately the rules of both have been forgotten, though we know that they were played without speaking, though not without laughter.
Word To Use Today: mumchance. This word arrived in the English language in the 16th century to mean a masquerade or a mime show. It comes from the Middle Low German mummenschanze which means masked serenade, from mummen (which comes from the Old French momen, mask) and schanze, which means chance.