1530s, "freedom from exaggeration, self-control," from 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, retiring demeanor, disinclination to presumption, unobtrusiveness" is from 1550s; that of "womanly propriety, purity or delicacy of thought or manner" is from 1560s.
In euery of these thinges and their semblable is Modestie; whiche worde nat beinge knowen in the englisshe tonge, ne of al them which under stode latin, except they had radde good autours, they improprely named this vertue discretion. [Sir Thomas Elyot, "The Boke Named The Gouernour," 1531]
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]
The pride which masks as modesty is the most perverse of all. [Marcus Aurelius]