certain

modif.

1. Confident

   assured, sure, positive, questionless, satisfied, self-confident, undoubting, unwavering, believing, secure, untroubled, unconcerned, undisturbed, unperturbed, convinced, assertive, cocksure; see also calm 1, confident 2.

2. Sure

   destined, determined, predestined; see inevitable.

3. Beyond doubt

   indisputable, unquestionable, assured, positive, real, true, genuine, plain, clear, undoubted, indubitable, guaranteed, unmistakable, unassailable, sure, incontrovertible, undeniable, definite, supreme, unqualified, infallible, undisputed, unerring, sound, reliable, trustworthy, evident, conclusive, decisive, unambiguous, authoritative, irrefutable, unconditional, incontestable, unquestioned, absolute, unequivocal, inescapable, in the bag*, on ice*; see also accurate 1.

   Antonyms doubtful, uncertain, dubious.

4. Dependable

   trustworthy, safe, sound; see reliable 2.

5. Fixed

   settled, concluded, set, agreed upon; see definite 1, determined 1.

6. Specific but not named

   special, marked, specified, defined, one, some, a few, a couple, several, appreciable, upwards of, regular, particular, singular, especial, precise, specific, express; see also definite 1, individual 1, special 1.

certain usually suggests conviction based on specific grounds or evidence this letter makes me certain of his innocence; suresuggests merely an absence of doubt or hesitancy I'm sure you don't mean it; confident stresses the firmness of one's certainty or sureness, esp. in some expectation she's confident she'll win; positive suggests unshakable confidence, esp. in the correctness of one's opinions or conclusions, sometimes to the point of dogmatism he's too positive in his beliefs

be certain

for certain