1. (v. t.) To give certain information to; to assure; to make certain.

2. (v. t.) To give certain information of; to make certain, as a fact; to verify.

3. (v. t.) To testify to in writing; to make a declaration concerning, in writing, under hand, or hand and seal.

OK accept accredit acknowledge affirm allege amen and candle approve ascertain assert assert under oath asseverate assure attest authenticate authorize autograph aver avouch avow back back up be sponsor for bear out bear witness bolster bond book buttress certificate charter cinch circumstantiate classify clear up clinch commission confirm corroborate cosign countersecure countersign decide declare depone depose determine disclose dismiss all doubt document empower enable endorse enfranchise ensure entitle establish find out fix fortify franchise get at give evidence give official sanction give permission give power give the go-ahead give the imprimatur give thumbs up guarantee guaranty initial insure kiss the book legalize legitimize license make certain make no doubt make no mistake make sure make sure of nail down notarize pass pass on pass upon patent permit privilege probate profess prove ratify reassure reinforce remove all doubt rubber stamp sanction say amen to seal second secure see that see to it set at rest settle sign sign and seal sign for sort out sponsor stand behind stand up for strengthen subscribe to substantiate support sustain swear swear and affirm swear by bell swear the truth swear to swear to God swear to goodness testify undergird undersign underwrite uphold validate verify visa vise vouch vouch for vouchsafe vow warrant witness