ump‧teenth /ˌʌmpˈtiːnθ◂/ adjective [only before noun]
[Date: 1900-2000; Origin: umpty 'many' (a joke word) (1900-2000) + -teenth (as in thirteenth)]
if something happens for the umpteenth time, it happens again after having happened many times before – used when you are annoyed that it has happened so often:
‘This is crazy,’ she told herself for the umpteenth time.

[TahlilGaran] Dictionary of Contemporary English ▲