contusion

湊 かなえの小説 "Confessions" を読んでいます。

Mother's body had a single stab wound to the belly and a contusion on the back of the head. They said that she was stabbed with a kitchen knife and then thrown down the stairs.

"contusion" は "stab" ではない傷と思われるので、打撲の跡と推測できますが、辞書で確認します。

・Oxford English Dictionary: an injury to part of the body that does not break the skin: There were multiple contusions and abrasions on his face and arm.
・Collins Dictionary: A contusion is a bruise.: She was treated for bruising and contusions.
・Cambridge English Dictionary: a bruise: This was the time when defendants received their injuries, consisting chiefly of abrasions and contusions.

"contusion" は "bruise" と同じ意味のようですが、次の辞書に丁寧な説明がありました。

・Vocabulary.com: Contusion is really just a fancy word for a bad bruise. Professional athletes are often benched suffering from contusions. After all, if they're being paid millions, it sounds kinda wimpy to pull them because they're suffering from a...bruise.
A contusion is any damage to the body that doesn't break the skin but ruptures the blood capillaries beneath, resulting in a handsome-looking discoloration. For once, it's a medical term not used widely to describe a broader emotional or psychological state. You could talk about an "emotional contusion," but please, better not to. There are better terms around (see heartbroken, wounded, forlorn, etc.). Your audience will thank you.