To Harm, To Injure, To Damage
transitive verb, godan verb
To do loss to something means you are doing something to make something have loss. This is to harm or to injure.
そこなう
In order to harm your opponent, you go way overboard. You soak (そこ) them in acid. Soaked head to toe. Too far man, too far.
働きすぎてあんたが健康を損なうんじゃないかって、心配してるのよ。
I’m worried that you may ruin your health by working too hard.