umpteenth

"I'll go to bed and I'll not get up for umpty-eleven months." You know the feeling. The speaker here is war-weary Bill, a character in Patrick MacGill's early 20th-century novel The Great Push. His "umpty" originated as military slang around 1905 and stood for an indefinite number, generally largish. (It was probably created by analogy to actual numbers such as "twenty.") Soon, there followed "umpteen," blending "umpty" and "-teen." "Umpteen" usually describes an indefinite and large number or amount, while the related "umpteenth" is used for the latest or last in an indefinitely numerous series. We only occasionally use "umpty" these days (and even more rarely "umptieth"), but you're bound to hear or read "umpteen" and "umpteenth" any number of times.