Drinker is from 'drink' + agentive '-er'. The verb 'drink' is from Old English 'drincan', from Proto-Germanic '*drinkaną'. The ancestry passes through Old English drincan and Proto-Germanic *drinkaną. The suffix -er marks an agent, instrument, or associated person, so the English form is shaped by recognizable word formation as well as by its inherited or borrowed base. In present use as a noun, it means "a person who drinks, especially one who consumes alcohol", keeping the historical formation close to the word's ordinary semantic work. Related words include drink, drank, drunk, and drench.