Umpteen is a term for an unspecified but reasonably large number, used in a humorous fashion or to imply that it is not worth the effort to pin down the actual figure. Despite the -teen ending, which would seem to indicate that it lies between 12 and 20, umpteen can be used in ways implying it is much larger than that—if it ever could be pinned down.
According to one dictionary, the word is derived from the slang ump(ty), a dash in Morse code (of imitative origin), plus -teen.
The Oxford English Dictionary reports its use in 1918, and offers the alternative spelling umteen. It agrees that the derivation is from umpty, whose etymology is given as "A fanciful verbal repr. of the dash (—) in Morse code."
Read more about this topic: Indefinite And Fictitious Numbers