I recently used the word "umpteenth" to describe something to my son's mother. It's a word I rarely use, but it got me thinking as to whether this word was actually a word or if it's just jargon.
Well, according to Merriam-Webster.com, "umpteen" is a word and it means "very many." It's a word often used informally to describe something that is occurring in large but unspecified quantities.
The word "umpteen" was first used in 1918 and it derives from the word "umpty," which was first used in 1905. Umpty was originally the Morse code slang for "dash."
Source: Wikipedia, Merriam-Webster.com, Etymonline.com