Confident; undoubting; having no fear of being deceived or disappointed.Certain of one's facts, position, or the like; fully persuaded; positive.Certain to find or retain: with of: as, to be sure of success; to be sure of life or health.Fit or worthy to be depended on; capable of producing a desired effect or of fulfilling requisite conditions; certain not to disappoint expectation; not liable to failure, loss, or change; unfailing; firm; stable; steady; secure; infallible.Certain to be or happen; certain.Undoubted; genuine; true.Out of danger; secure; safe.Engaged to marry; betrothed.See to be sure, below.To make fast by betrothal; betroth.Synonyms and Certain, Positive, etc. See confident.Certainly; without doubt; doubtless; surely.Firmly; securely.To assure; make certain.