SWEAR BY

{v.} 1. To use as the support or authority that what you are saying is truthful; take an oath upon. * /A witness swears by the Bible that he will tell the truth./ * /In ancient Greece a doctor swore by Apollo, the god of healing, that he would be a good doctor./ * /John swore by his honor he would return the bike./ 2. To have complete confidence in; be sure of; trust completely. * /When John has to go somewhere fast, he swears by his bike to get there./ * /We can be sure that Fred will come on time, since his friend Tom swears by him./