beam: [OE] In Old English times the word bēam (like modern German baum) meant ‘tree’ – a signification preserved in tree-names such as hornbeam and whitebeam. But already before the year 1000 the extended meanings we are familiar with today – ‘piece of timber’ and ‘ray of light’ – had started to develop. Related forms in other Germanic languages (which include, as well as German baum, Dutch boom, from which English gets boom ‘spar’ [16]) suggest a West Germanic ancestor *bauma, but beyond that all is obscure. => boom
