Definition of "forewarn"

And ſure, although it was invented to eaſe his mynde of griefe, there be a number of caveats therein to forewarne other young gentlemen to foreſtand with good government their folowing yl fortunes; […]

1576, George Whetstone, “The Ortchard of Repentance: […]”, in The Rocke of Regard, […], London: […] [H. Middleton] for Robert Waley; republished in J[ohn] P[ayne] Collier, editor, The Rocke of Regard, […] (Illustrations of Early English Poetry; vol. 2, no. 2), London: Privately printed, page 291

“I came down like a wolf on the fold, didn’t I ? Why didn’t I telephone ? Strategy, my dear boy, strategy. This is a surprise attack, and I’d no wish that the garrison, forewarned, should escape. […]”

1913, Robert Barr, chapter 4, in Lord Stranleigh Abroad