Certain

[estar] certero

(sure, positive, not doubting)

[estar] cierto

(sure, positive, not doubting)

certero

(sure, positive, not doubting)

cierto

(not specifically named, indeterminate, indefinite)

definitivo

(sure, positive, not doubting)

determinado

(sure, positive, not doubting)

seguro

(sure, positive, not doubting)

tener la certeza [de]

(sure, positive, not doubting)

tener la certidumbre [de]

(sure, positive, not doubting)

tener la certitud [de]

(sure, positive, not doubting)