An Etymological Dictionary of the German Language/tapfer
tapfer, adj., ‘brave, variant, bold,’ from MidHG. tapfer (dapfer, tapfel), ‘firm, pressed, full, weighty, important’ (only in late MidHG. brave), OHG. tapfar, ‘heavy, weighty, important’; comp. Du. dapper, ‘brave, much,’ E. dapper. The connection in meaning with OSlov. doblĭ, ‘strong, able,’ debelŭ, ‘stout,’ and dobrŭ, ‘beautiful, good,’ is quite clear, but it is difficult to show how it is related to the corresponding OIc. dapr, ‘sad’; note, however, ModHG. dreist, ‘bold, audacious,’ OHG. drîsti, OLG. thrîsti, compared with Lat. trîstis.