tkday
n. A person's 10,000th day since birth. Also: 10K day.

Example Citations:
Approaching his tkday — or 10,000th day on Earth — Horne decided he wanted to leave a permanent mark on history, and as a lover of language and devout Countdown fan, he decided that the best way to do that would be to get a new word into the dictionary.
—Steve Bennett, "Wordwatching by Alex Horne," Chortle, January 14, 2010

The 10k Day celebration — alternately called "Tkday" or "decimal birthday" — has become the new coming-of-age for Generation Y.
—Paola Loriggio, "Happy 10,000th day — let's party," The Toronto Star, February 23, 2008

Earliest Citation:
You'll reach your Tkday when you're about 27 years, 3 months and 15 days.
—V.G. Farmer, "Tkday," Urban Dictionary, October 25, 2006

Notes:
The domain name tkday.com was registered on October 3, 2006.

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