To make certain that something will happen or be the case.
From Old French *enseurer* ('to assure, make safe'), from *en-* ('make') + *seur* ('sure'), from Latin *securus* ('safe, secure'). It is closely related to *insure* and *assure*, which later took on more specific uses.
To 'ensure' is to move something from 'probably' to 'definitely' in your mind. The word is about building conditions so strong that chance has almost no room to play.
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