1560s, "appropriateness, state or quality of being fit or suitable," from Latin decentia "comeliness, decency," from decentem "becoming, fitting," present participle of decere "to be fitting or suitable," from PIE *deke-, from root *dek- "to take, accept." Meaning "modesty, freedom from ribaldry or obscenity" (i.e. "appropriateness to standards of society") is from 1630s.
