expression, godan verb (-ku)
cut off a sleeping person's head; assassinate someone in their sleep
Literal meaning: to kill a sleeping person by cutting their neck. Often used in historical or dramatic contexts.
戦国時代には、寝首をかくような卑怯な手も使われた。
In the Warring States period, cowardly tactics like cutting off a sleeping person's head were also used.
expression, godan verb (-ku)
catch someone off guard by setting traps; stab someone in the back
Figurative extension: to betray or ambush someone who trusts you, often through scheming or traps. Implies underhandedness.
彼は親友に寝首をかかれて、会社を追われた。
He was stabbed in the back by his close friend and forced out of the company.
油断していると、ライバルに寝首をかかれるぞ。
If you let your guard down, your rivals will catch you off guard.