Definition of "seventieth" [sev•en•ti•eth]

• The ordinal number matching the number 70 in a series. (noun)
• One of 70 equal parts. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The seventieth is the consummation of the preceding ones, as the"
• "The first time I talked about the “five rules for the evolution of cooperation” was at a conference held in March 2006 at the Zoology Department at the University of Oxford in honor of the seventieth birthday of my great friend and mentor, Lord May of Oxford."
• "The seventieth anniversary of Britain's entry into WWII following Germany's invasion of Poland on the 1st of September 1939 sees its surviving participants in their eighties and nineties."