Umpteenth (adjective)

Indicating an unspecified large number of times or instances; countless or numerous.

Origin:

From the word umpteen which means "a large number, many", of uncertain origin.

Examples:

1. I've told you the instructions for the task on the umpteenth time.
2. We"ve been through this umpteen times, and I"m still not convinced.
3. I"ve been to this exhibition on my umpteenth visit and it"s still as interesting as the first time.
4. She"s asked me the same question for the umpteenth time, and I"m starting to get annoyed.
5. I've read that book for the umpteenth time and it never gets old.