birch (n.)
Old English berc, beorc (also the name of the rune for "b"), from Proto-Germanic *berkjon (cognates: Old Saxon birka, Old Norse börk, Danish birk, Swedish björk, Middle Dutch berke, Dutch berk, Old High German birihha, German Birke), from PIE *bhergo (cognates: Ossetian barz, Old Church Slavonic breza, Russian bereza, Lithuanian beržas, Sanskrit bhurjah, Latin farnus, fraxinus "mountain ash"), from root *bhereg- "to gleam, white." Meaning "bunch of birch twigs used for flogging" (1640s) led to verb meaning "to flog" (1830). Related: Birched; birching. Birch beer is by 1827, American English.