An Etymological Dictionary of the German Language/Annotated/eben
eben, adjective, ‘even, level, plain, smooth,’ from Middle High German ëben, Old High German ëban, adjective, ‘level, flat, straight’; common to Teutonic under these meanings, but it is not found in any other Aryan group; compare Old Saxon eƀan, Dutch even, Anglo-Saxon ëfn, English even, Old Icelandic jafn, Gothic ibns, ‘level.’ Akin perhaps to Gothic ibuks, adjective, ‘backward’ (see Ebbe). Apart from Teutonic the stem ib in the form ep or ebh has not yet been authenticated; Latin œ̂quus (Sanscrit êka), cannot, on account of phonetic differences, be regarded as a cognate. —
eben, adverb, ‘even, just,’ from Middle High German ëbene, Old High German ëbano; compare Old Saxon ëfno, Anglo-Saxon ëfne (whence English even); the old adverb form of the adjective (Compare neben.)