Certain grueling race, informally (3)
I believe the answer is:
tri
(Other definitions for tri that I've seen before include "Three-point" , "Prefix indicating three" , "Prefix meaning three" , "Prefix denoting three" , "Denotes three" .)
I believe the answer is:
tri
(Other definitions for tri that I've seen before include "Three-point" , "Prefix indicating three" , "Prefix meaning three" , "Prefix denoting three" , "Denotes three" .)