The term 'trigger-happy' is a modern American English compound, first recorded in the mid-20th century. It combines 'trigger', the lever on a firearm that initiates firing, with 'happy' in its informal sense of 'inclined to' or 'pleasantly eager'. The literal construction paints a vivid picture of someone who finds eagerness or pleasure in pulling a trigger. This concrete, potentially lethal imagery was then extended metaphorically to describe anyone who is recklessly eager to initiate any decisive or damaging action.

Structure: trigger + happy - trigger: From Dutch trekker (that which pulls, a trigger). In this compound, it functions as a noun denoting the mechanism of a firearm. - happy: From Middle English hap (chance, luck, fortune). In this compound, it functions as an adjective meaning 'inclined to' or 'characterized by'.