Source : Webster's Revised Unabridged Dictionary (1913)

Certitude \Cer"ti*tude\, n. [LL. certitudo, fr. L. certus: cf.
   F. certitude. See {Certain}.]
   Freedom from doubt; assurance; certainty. --J. H. Newman.

Source : WordNet®

certitude
     n : total certainty or greater certainty than circumstances
         warrant [syn: {cocksureness}, {overconfidence}]