ensure

To make sure or certain of something (usually some future event or condition).

I use an alarm clock to ensure that I get up on time.

British journalists shun complete respectability, feeling a duty to be ready to savage the mighty, or rummage through their bins. Elsewhere in Europe, government contracts and subsidies ensure that press barons will only defy the mighty so far.

To make a pledge to (someone); to promise, guarantee (someone of something); to assure.

Thenne he cryed hym mercy and sayd Faire knyght for goddes loue slee me not / and I shall ensure the neuer werre ageynst thy lady / but be alwey toward her / Thenne Bors lete hym be