Swim-bike-run race, for short (3)

I believe the answer is:

tri

(Other definitions for tri that I've seen before include "Denotes three" , "Prefix indicating three" , "Prefix denoting three" , "Prefix meaning three" , "Three-point" .)

I've seen this clue in the Universal, the USA Today, the LA Times, The Wall Street Journal and The New York Times.

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