Etymology
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better (adj., adv.)

Middle English bettre, from Old English bettra, earlier betera "of superior quality or excellence," from Proto-Germanic *batizo-, perhaps from PIE *bhad- "good," but Boutkan finds no good IE etymology. For etymology and evolution, see best. Cognate words also have become the comparative adjective of good in the older Germanic languages (Old Frisian betera, Old Saxon betiro, Old Norse betr, Danish bedre, Old High German bezziro, German besser, Gothic batiza). All are comparatives of a positive (Proto-Germanic *bat) which is not in use.

In Middle English the adverbial form commonly was bet, sometimes also used an adjective; bet was displaced by c. 1600. Better is attested from late Old English as "improved in health, more healthy" (adv.); from late 12c. as "more useful or desirable." Better half "wife" is attested from 1570s.

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better (n.1)

late 12c., "that which is better," from better (adj.). The specific meaning "one's superior" is from early 14c. The better "improvement" (as in for the better) is from 1690s. To get the better of someone "obtain mastery or victory over" is from 1650s, from better in a sense of "superiority, mastery," which is recorded from mid-15c. Related: Betters.

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better (v.)

Old English *beterian "improve, amend, make better," from Proto-Germanic *batizojan (source also of Old Frisian beteria, Dutch beteren, Old Norse betra, Old High German baziron, German bessern), from *batizo- (see better (adj.)). The meaning "exceed, surpass, outdo" is from 1540s. Related: Bettered; bettering.

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betterment (n.)

"improvement," 1590s, from better (v.) + -ment.

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bettermost 

"best," 1743, jocular, from better (adj.) + -most.

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boot (n.2)

"profit, use," Old English bot "help, relief, advantage; atonement," literally "a making better," from Proto-Germanic *boto (see better (adj.)). Compare Old Frisian bote "fine, penalty, penance, compensation," German Buße "penance, atonement," Gothic botha "advantage, usefulness, profit." Now mostly in phrase to boot (Old English to bote), indicating something thrown in by one of the parties to a bargain as an additional consideration.

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bettor (n.)

"one who lays a wager," c. 1600, also better, agent noun from bet (v.). The form is unusual; OED notes that English agent nouns in -er tend to shift toward -or as their senses become more specific; in this case it also might have been done to steer clear of better (n.1) and thus avoid confusion.

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bet (n.)

1590s, "the mutual pledging of things of value to be won or lost based on some future event," appearing simultaneously with the verb, originally in the argot of petty criminals, a word of unknown origin.

Perhaps it is a shortening of abet or else from obsolete beet "to make good" (related to better), if the original notion is "to improve" a contest by wagering on it, or to encourage a contestant. Or perhaps the word is from the "bait" sense in abet. The meaning "that which is wagered" is from 1796.

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-er (2)

comparative suffix, from Old English -ra (masc.), -re (fem., neuter), from Proto-Germanic *-izon (cognates: Gothic -iza, Old Saxon -iro, Old Norse -ri, Old High German -iro, German -er), from PIE *-yos-, comparative adjective suffix. Originally also with umlaut change in stem, but this was mostly lost in Old English by historical times and has now vanished (except in better and elder).

For most comparatives of one or two syllables, use of -er seems to be fading as the oral element in our society relies on more before adjectives to express the comparative; thus prettier is more pretty, cooler is more cool [Barnhart].
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