1. What does it mean?
잠수이별 combines going silent, 잠수, with breaking up. It describes a partner effectively ending the relationship by cutting off communication, leaving the other person without a clear conversation.
Also written or said as jamsuibyeol
2. The nuance
A delayed reply alone is not enough to establish a breakup. The term describes a relationship-ending pattern; it is not a reason to ignore boundaries or repeatedly pursue someone who has asked for no contact.
3. Examples
“소설 속 주인공은 잠수이별을 겪고 답 없는 연락을 그만 기다렸어.”
After being ghosted by their partner in the novel, the protagonist stopped waiting for a reply.
“연락이 하루 늦었다고 바로 잠수이별이라고 생각하지는 않았어.”
I didn't immediately assume the relationship was over just because a reply was a day late.
Sources
Sinjoeo Korean Slang Dictionary
References support the meaning and usage. Example sentences are written for NoCapWiki.