Definition of "500th" [500th]

• The ordinal number of five hundred in counting order (adjective)

WordNet. Princeton University. 2010.

• "My 500th was the Tri for Fun Triathlon in Pleasanton, in August."
• "Publishing | An article marking the 500th issue of MAD Magazine notes the milestone brings with it dwindling circulation and a shift to a quarterly schedule."
• "* Speaking of big milestones, Evan Dorkin says the 500th issue of Mad Magazine is out on newsstands now, which is kind of amazing -- to me at any rate."