铤而走险 is a four-character idiom formed from the characters 铤 (meaning to hurry or rush), 而 (a grammatical particle that links actions), 走 (meaning to run or flee), and 险 (meaning danger or peril). It originates from the classical text "Zuo Zhuan" where the phrase literally denotes hurrying into danger, constructed by combining the sense of rapid movement from 铤 and 走 with the hazardous outcome from 险, linked by 而 to express acting recklessly under desperation.