Tridecennary

tridecennary (try-di-SEN-uh-ree) noun

1. A period of thirteen years.

2. A thirteenth anniversary.

[From Latin tres (three), from decem (ten) + annus (year).]

I'm a subscriber of A.Word.A.Day ( not that it does me much good! Though, admittedly, I don't really get time to go through the mails properly, so... ). Anyway, last week's theme was the number 13, as it was their thirteenth anniversary. This was the first word and Anu Garg mentioned that Google showed only one hit for this word. I'd run a search for it at that time and seen 3 results; the original plus the Wordsmith site. And a search now shows about 668 results ( with Wordsmith at the top! )

As a Sally Boyson noted in the AWADmail Issue 253, it is a great example of Heisenberg’s Uncertainty Principle which states that you can't observe something without affecting it in someway. Of course, it also reflects the immense popularity of A.Word.A.Day!