Definition of assure :
1. To affiance; to betroth.
2. To confirm; to make certain or secure.
3. To declare to, solemnly; to assert to ( any one) with the design of inspiring belief or confidence.
4. To insure; to covenant to indemnify for loss, or to pay a specified sum at death. See Insure.
5. To make sure or certain; to render confident by a promise, declaration, or other evidence.
go over, predict, prognosticate, fit, see, cover, master, hear, check into, batten, implement, persuasion, go out, sanction, learn, hold, retard, hearten, narrate, delay, procure, manipulate, ice, take in, cinch, tell apart, comfort, put something into action, reinforce, enforce, chequer, discipline, construe, put/bring/carry something into effect, carry through, discover, cheer, attend, secern, date, check over, arrest, adopt, reckon, tell, foretell, secernate, batten down, go through, convince, figure, visualize, distinguish, consider, plug, go through with, jibe, correspond, view, progress, differentiate, crystallize, tick, order, solace, come across, meet, visualise, hold back, call, reassure, contain, match, check off, solidify, stop, tally, console, settle, command, understand, turn back, realize, stop up, checker, say, tick off, examine, severalise, moderate, run into, evidence, make certain, run across, enjoin, certain, realise, look, uphold, undertake, separate, soothe, hold in, severalize, condition, fancy, project, crystalize, watch, take care, recite, inspirit, check up on, envision, mark, keep in line, check out, gel, image, get word, witness, recount, crack, go steady, visit, break, catch, escort, operate, gibe, win over, train, guaranty, mark off, forebode, look into, fasten, underline, satisfy, encourage, pick up, persuade, see to it, picture, get a line, anticipate, encounter, find, experience, curb, suss out, control, get wind, underwrite, interpret, regard, strengthen, fix
affirm (part of speech: verb)
profess, propound, accept, ratify, pledge, validate, contend, certify, admit, declare, promise, corroborate, express, maintain, sustain, submit, endorse, attest, warrant, verify, claim, acknowledge, testify, adjure, approve, affirm, support, proclaim, state, avouch, aver, pronounce, assert, set down
guarantee (part of speech: verb)
promise (part of speech: verb)
ascertain (part of speech: verb)