One of two in a tournament (4)
I believe the answer is:
semi
'one of two in a tournament' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for semi that I've seen before include "Common type of house" , "Prefix meaning half (4)" , "Property attached to another" , "House; match" , "House attached to one other" .)