before 900;Middle Englishbettre,Old Englishbet(t)(e)ra; cognate with Old High Germanbezziro (Germanbesser), Dutchbeter,Old Norsebetr,Gothicbatiza, equivalent to bat- (cognate with Old High Germanbaz (adv.) better; akin to boot2) + -iza comparative suffix; suggested relation to Sanskritbhadrá- “fortunate” is doubtful. See best
10. amend; advance, promote; reform, correct, rectify. See improve.
O.E. betera (see best), from P.Gmc. *batizo-, from PIE *bhad- "good." Comparative adj. of good in the older Gmc. languages (cf. O.N. betr, Dan. bedre, Ger. besser, Goth. batiza). Superseded bet in the adverbial sense by 1600. Better half "wife" is first attested 1570s; to get the better of (someone) is from mid-15c.