To lose a quarrel or argument; to be unable to talk one's way through and be talked down by the other person.
議論の途中で論点がずれて、彼は結局言い負けてしまった。
During the debate the points got off track and he eventually lost the argument.
彼女は相手の強い反論に圧されて言い負けたようだ。
She seemed to have been overwhelmed by the other's strong rebuttal and lost the argument.
上司の前では反論しづらく、つい言い負けてしまうことが多い。
It's hard to object in front of a boss, so I often end up losing the argument.