以血洗血yǐ xuè xǐ xuè

wash blood with blood—avenge oneself by killing the enemy
❍ 汝国已杀突董等，吾又杀汝，犹～，污益甚尔。吾今以水洗血，不亦善乎！ (《旧唐书·源休传》) Your country has killed our Tu Dong and others. If we kill you in return,it will be like washing blood with blood which is more harmful. I’ll be kind enough if I wash blood with water today.

• sub-
• sub
• sub
• subaltern
• subatomic
• sub-committee
• subconscious
• subcontinent
• subcontract
• subcutaneous
• subdivide
• subdue
• subedit
• subfusc
• subheading
• subhuman
• subject
• subject
• subject
• subjective
• subjoin
• sub judice
• subjugate
• subjunctive
• sublease