emotional scar; mental trauma
Refers to lasting psychological pain or damage, similar to a wound of the heart. Often used in contexts of past abuse, betrayal, or deep disappointment.
She suffered emotional scars from being bullied as a child.
Those words reopened his emotional wounds.
Compound of 心 (こころ, 'heart, mind') + の (possessive particle) + 傷 (きず, 'wound, injury'). Literally 'wound of the heart'. The metaphorical extension to emotional pain is straightforward and long-established.