say it: SUR-tuhn-tee
certainty is a noun meaning "the state of being certain". It carries 2 recorded senses.
the state of being certain
“his certainty reassured the others”
something that is certain
“his victory is a certainty”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for certainty come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.