'Despair' in the Bible

And David said in his heart, I shall now perish one day by the hand of Saul: there is nothing better for me than that I should escape into the land of the Philistines; and Saul will despair of me, to seek me any more in all the borders of Israel: so shall I escape out of his hand.

Therefore I turned about to cause my heart to despair concerning all the labor wherein I had labored under the sun.