From Middle English acorn, an alteration (after corn) of earlier *akern, from Old English æcern (“acorn, oak-mast”), from Proto-West Germanic *akarn, from Proto-Germanic *akraną, from Proto-Indo-European *h₂égrō (“berry”). Cognate with Scots aicorn, Saterland Frisian Äkkene, Dutch aker (“acorn”), German Ecker (“acorn”), Danish agern (“acorn”), Faroese, Icelandic akarn (“acorn”), Norwegian Nynorsk åkorn (“acorn”), Tocharian B oko (“fruit”), Welsh eirin (“plums”), Breton irin (“plum”), Irish airne (“sloe”), Lithuanian úoga, Russian я́года (jágoda, “berry”), etc. Not related to Old English āc (“oak”), corn (“corn, seed”) or Middle English acquerne.