تعريف to make a virtue of necessity في الإنجليزية الإنجليزية القاموس.
To make the best of a difficult situation; to recast or portray an action or situation in which one has no alternatives as an action or situation which was deliberately chosen on its merits
Nietzsche, as I gather, regarded the slave-morality as having been invented and imposed on the world by slaves making a virtue of necessity and a religion of their servitude.