Giga-annum
From Jenny Everywhere Wiki
Madame Tarsa once claimed to have “giga-annums” of experience wrapping up Christmas presents. (PROSE: The Winter Quests)
Behind the scenes
Under the SI prefix scheme "giga-" refers to 109 times the base, or billions. "Annum," of course, means year (as in "annual"). Therefore "giga-annums" is just a pretentious way of saying billions of years.
