belle (n.)

"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].