billennia

a new word meaning 'billions of years,' billennia is appearing informally in science writing in phrases such as 'countless billennia' or 'the billennia of evolutionary time.' The word billennium was coined for another purpose, however; it is a registered trademark of the Billennium® Organizing Committee and is used, in the words of a committee ......
Found on http://www.unc.edu/~rowlett/units/dictB.html
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