Acorns. So called from the oak trees of Chaonia or Dodona. Some think beech-mast is meant, and tell us that the bells of the oracle were hung on beech-trees, not on oaks.
The Greek word is fhgoz; Latin, fagus. Hence Strabo, Dwdwuhu, fhgou te Pelasgwu edrauou hkeu (He to Dodona came, and the hallowed oak or beech [fagus ], the seat of the Pelasgi.) Now, “fagus” means the food-tree, and both acorns and mast are food, so nothing determinate can be derived from going to the root of the word, and, as it is extremely doubtful where Dodona was, we get no light by referring to the locality. Our text says Chaonia (in Epirus), others place it in Thessaly.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894