The word "一吐为快" is formed by sequentially combining the character "一" (meaning "once" or "one") to indicate a single action, "吐" (meaning "to spit out" or metaphorically "to vent") to denote the act of expressing, "为" (meaning "as" or "to be") to link the action to its outcome, and "快" (meaning "pleasure" or "relief") to specify the resulting state, thus constructing a fixed idiom that literally translates to "once vent as pleasure" and conveys the concept of finding relief by speaking out.