纵虎归山放虎归山zòng hǔ guī shān

let the tiger return (/go back)to the mountains—cause calamity for the future;allow the enemy to escape
❍ 前在长安，见安禄山面有反相，知其包藏祸心，不想圣上命彼出镇范阳，分明～。(洪昇《长生殿》) When l was in the capital I saw that An Lushan looked like a rebel and knew that he was plotting mischief; but then the emperor suddenly sent him to command Fanyang—this is like letting the tiger go back to the mountain.
❍ 哼！假如我们捉到瑞澂同黎元洪、张彪他们，那就不会～。(李六如《六十年的变迁》 Ⅰ—250) Well,if we ever lay our hands on Rui Zhang,Li Yuanhong or Zhang Biao,we’ll never let them off so easily. That would amount to setting a captured tiger free…

• unveil
• unveracious
• unversed
• unwaged
• unwanted
• unwares
• unwarrantable
• unwary
• unweighed
• unweighted
• unwelcome
• unwholesome
• unwieldly organizations
• unwieldy
• unwilling
• unwind
• unwish
• unwit
• unwittingly
• unworkable
• unworthiest
• unworthiness
• unworthy
• unwritable
• unwritten