1530s, "freedom from exaggeration, self-control," from Middle French modestie or directly from Latin modestia "moderation, sense of honor, correctness of conduct," from modestus "moderate, keeping due measure, sober, gentle, temperate," from modus "measure, manner" (from PIE root *med- "take appropriate measures"). Meaning "quality of having a moderate opinion of oneself" is from 1550s; that of "womanly propriety" is from 1560s.
La pudeur donne des plaisirs bien flatteurs à l'amant: elle lui fait sentir quelles lois l'on transgresse pour lui;
(Modesty both pleases and flatters a lover, for it lays stress on the laws which are being transgressed for his sake.) [Stendhal "de l'Amour," 1822]