"beautiful woman well-dressed; reigning beauty," 1620s, from French belle, from Old French bele, from Latin bella, fem. of bellus "beautiful, fair," from PIE *dwenelo-, diminutive form of root *deu- (2) "to do, perform; show favor, revere." "The dim. meaning is the reason why bellus was originally used to refer to women and children; it was applied to men only ironically" [de Vaan].

French, literally "a great heap" (13c.), from beau "fine, great" (see beau (n.)) + coup "a stroke," also "a throw," hence, "a heap" (see coup (n.)). Compare Spanish golpe "multitude," also "a punch, hit," from the same Latin source.

"beautifulness or excellence as an abstract ideal," 1801, from French beau idéal "the ideal beauty, ideal excellence," in which beau is the subject, but as English word-order usually has the adjective first, the sense has shifted in English toward "perfect type or model." Compare beau + ideal.

also beau monde, "the fashionable world," 1714, French, from beau (see beau) + monde, from Latin mundus "world" (see mundane).

"elegant literature, literature as fine art," 1710, French, literally "fine letters," from belles, plural of belle, fem. of beau "fine, beautiful" (see beau) + lettres, plural of lettre "letter" (see letter (n.)). The literary equivalent of beaux arts; its boundaries never have been exact, and it is "now generally applied (when used at all) to the lighter branches of literature, or the æsthetics of literary study" [OED].

Proto-Indo-European root meaning "to do, perform; show favor, revere."

It forms all or part of: beatific; beatify; beatitude; Beatrice; beau; beauty; Bella; belle; beldam; belladonna; belvedere; bene-; benedict; Benedictine; benediction; benefactor; beneficiary; benefice; beneficence; benefit; benevolent; benign; bonanza; bonbon; bonhomie; bonito; bonjour; bonny; bonus; boon (adj.); bounty; debonair; embellish.

It is the hypothetical source of/evidence for its existence is provided by: Latin bene (adv.) "well, in the right way, honorably, properly," bonus "good," bellus "handsome, fine, pretty," and possibly beatus "blessed," beare "to make blessed."