'acock' originates from Middle English, specifically the word 'a-cok,' where 'a-' meant 'on' and 'cok' referred to a rooster, symbolizing pride or defiance.

'a-cok' transformed into the modern English word 'acock' through Middle English usage.

Initially, it meant 'in a cocky or proud manner,' and this meaning has largely remained the same in modern usage.