An Etymological Dictionary of the German Language/Annotated/Wehr
Wehr, feminine, ‘defence, resistance, protection,’ from Middle High German węr, Old High German węrî, feminine, ‘defence, fortification’; allied like Modern High German Wehr, neuter, ‘dam, weir,’ late Middle High German węr, neuter, ‘weir,’ to wehren, ‘to protect, defend; hinder, prevent, oppose, forbid.’ This verb is from Middle High German węrn, węrgen, Old High German węrian, węren, weak verb, ‘to hinder, protect, defend’; compare Gothic warjan, ‘to forbid, hinder,’ Old Saxon werian, ‘to hinder.’ On account of the meaning, its connection with wahren (root wor, ‘to look on,’ in Greek όράω) is not so apparent as its primitive kinship with the Sanscrit root vṛ, ‘to check, restrain, hinder.’