The story
- Middle English · inherited fromat do“to do”
- English todayado
From Northern Middle English at do (“to do”), infinitive of do, don (“to do”), see do. Influenced by an Old Norse practice of marking the infinitive by using the preposition at, att (compare Danish at gå (“to go”)). More at at, do.
Etymology from Wiktionary, CC BY-SA 4.0.