Definition of "inviolable"

But come, for thou, be ſure, ſhalt give account / To him who ſent us, whoſe charge is to keep / This place inviolable, and therefore theſe from harm.

1667, John Milton, “Book IV”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, lines 842–844

But honeſt men’s words are Stygian oaths, and promiſes inviolable.

a. 1682, Sir Thomas Browne, “Christian Morals”, in Henry Gardiner, editor, Religio Medici, together with a Letter to a Friend on the Death of His Intimate Friend and Christian Morals, London: W. Pickering, published 1845, part III, page 337

One more request, and I am lost, / If you its earnest prayer deny ; / It is, that you preserve the most / Inviolable secrecy / As to my plan.

1828, Thomas Castaly, “The Recorder”, in Fanny with Other Poems, page 87

"Now, Mr. Jones, having obtained your promise of inviolable secrecy, I come down to the essential point."

1929, Sir Arthur Conan Doyle, When the World Screamed‎