adjective
1.
( disapproving ) ( of an argument, opinion, etc. ) showing only one side of the situation; not balanced
SYN biased :
The press were accused of presenting a very one-sided picture of the issue.
2.
( of a competition or a relationship ) involving people who have different abilities; involving one person more than another :
a totally one-sided match
a one-sided conversation (= in which one person talks most of the time)