by 1907, popularized in World War I army slang, from umpty + -teen. Related: Umpteenth.
Entries linking to umpteen
umpty
1905, "of an indefinite number," originally Morse code slang for "dash," influenced by association with numerals such as twenty, thirty, etc.
-teen
word-forming element making cardinal numbers from 13 to 19, meaning "ten more than," from Old English -tene, -tiene, from Proto-Germanic *tekhuniz (cognates: Old Saxon -tein, Dutch -tien, Old High German -zehan, German -zehn, Gothic -taihun), an inflected form of the root of ten; cognate with Latin -decim (source of Italian -dici, Spanish -ce, French -ze).