I believe the answer is:
'unilateral' is the definition.
(I know that unilateral can be written as one-sided)
This is all the clue.
(Other definitions for one-sided that I've seen before include "Unfair or uneven" , "So denied being unfair or biased" , "Grossly unequal; biased" , "So denied being partisan or unfair" , "Unfair or partisan - single dimension?" .)