Definite; fixed: set aside a certain sum each week. Sure to come or happen; inevitable: certain success. Established beyond doubt or question; indisputable: What is certain is that every effect must have a cause. Capable of being relied on; dependable: a quick and certain remedy. Having or showing confidence; assured. Not specified or identified but assumed to be known: felt that certain breeds did not make good pets. Named but not known or previously mentioned: a certain Ms. Johnson. Perceptible; noticeable: a certain charm; a certain air of mystery. Not great; calculable: to a certain degree; a certain delay in the schedule. An indefinite but limited number; some: Certain of the products are faulty. for certain Without doubt; definitely.