1580s, "outrageous conduct," from Latin indecentia "unseemliness, impropriety," abstract noun from indecentem "unbecoming" (see indecent). Now especially of conduct which violates recognized standards of propriety (1690s).
incursion
incus
indear
indearing
indebted
indecency
indecent
indecipherable
indecision
indecisive
indeclinable