An Etymological Dictionary of the German Language/Buche
Buche, f., ‘beech, beech-tree,’ from the equiv. MidHG. buoche, OHG. buohha; AS. bôc-treów, with the collateral form bêce (from boeciae), E. beech. The form bôc has been preserved in E. buckmast, buckwheat; comp. OIc. bók, Goth. *bôka, ‘beech.’ The name of the tree is derived from pre-Teut.; according to Lat. fâgus, ‘beech,’ and Gr. φᾶγός, φηγός, its Europ. form would be bhâgos. The Gr. word signifies ‘edible oak.’ This difference between the Gr. word on the one hand and the Teut.-Lat. on the other has been explained “by the change of vegetation, the succession of an oak and a beech period”; “the Teutons and the Italians witnessed the transition of the oak period to the beech period, and while the Greeks retained φηγός in its orig. signification, the former transferred the name as a general term to the new forests which grew in their native wastes.” Comp. Eiche. Buche is properly ‘the tree with edible fruit’ (comp. Gr. φαγεῖν, ‘to eat,’ and φηγός), and hence perhaps the difference of meaning in Gr. may be explained from this general signification, so that the above hypothesis was not necessary.