/ ˌʌmpˈtiːn; NAmE / determiner
( informal ) very many :
I've told this story umpteen times.
► ump·teen pronoun :
Umpteen of them all arrived at once.
► ump·teenth / ˌʌmpˈtiːnθ; NAmE / determiner :
'This is crazy,' she told herself for the umpteenth time (= she had done it many times before) .
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WORD ORIGIN
early 20th cent.: humorous formation based on -teen .