Word of the day: Despite being in active use since the early 20th century, "umpteen" remains one of the most misunderstood and underused informal words in modern English. Most people have heard it. Few use it correctly. Even fewer know its fascinating military origin or how to naturally weave it into professional writing. Umpteen is an informal adjective and determiner in English. It means an indefinitely large but unspecified number — essentially "very many" or "countless." You use it when the exact number is unknown, unimportant, or so large it feels overwhelming to count.