An Etymological Dictionary of the German Language/Block
Block, m., ‘block, log, prison,’ from MidHG. bloch, ‘log, plant, a sort of trap.’ In the latter signification (to which MidHG. blocken, ‘to put in prison,’ is related) it represents OHG. bilóh (with syncopated i; see other similar examples under bei), ‘lock-up,’ which belongs to an OTeut. str. vb. lûkan, ‘to lock’ (comp. further E. lock; see Loch). The meaning ‘log, plank’ (MidHG. bloch), is probably based on a different word, which is most likely related to Balken; even in OHG., bloh occurs. The cognates passed into Rom. (Fr. bloc, bloquer), whence again ModHG. blockieren, E. to block.