killing

Should true Proportion ev'ry Mortal grace, / And Semetry be seen in ev'ry Face: / Beauty no longer would be thought divine, / Nor would its Charms with half the Lustre shine: / No courtly Dame a killing Look could boast, / If once the Foils of Homeliness were lost.

Livia found her ‘killing’, and derived such amusement from her Martinique French that he was forced to enjoy her as well.