An Etymological Dictionary of the German Language/Wehr
Wehr, f., ‘defence, resistance, protection,’ from MidHG. węr, OHG. węrî, f., ‘defence, fortification’; allied like ModHG. Wehr, n., ‘dam, weir,’ late MidHG. węr, n., ‘weir,’ to wehren, ‘to protect, defend; hinder, prevent, oppose, forbid.’ This verb is from MidHG. węrn, węrgen, OHG. węrian, węren, wk. vb., ‘to hinder, protect, defend’; comp. Goth. warjan, ‘to forbid, hinder,’ OSax. werian, ‘to hinder.’ On account of the meaning, its connection with wahren (root wor, ‘to look on,’ in Gr. όράω) is not so apparent as its primit. kinship with the Sans. root vṛ, ‘to check, restrain, hinder.’