'wallop' originates from Middle English, specifically the dialectal verb 'walopen' (or similar imitative forms), where the form likely echoed the sound or action of striking.

'wallop' changed from Middle English dialect forms such as 'walopen' and related onomatopoeic verbs, eventually becoming the modern English word 'wallop'.

Initially, it meant 'to strike or beat' (an echoic/imitative sense), and over time it retained that primary meaning while also extending to senses like 'a heavy defeat' and a slang noun for an alcoholic drink.