Толковый словарь английского языка Oxford English Reference - certainty

n. (pl. -ies) 1 a an undoubted fact. b a certain prospect (his return is a certainty). 2 (often foll. by of, or that + clause) an absolute conviction (has a certainty of his own worth). 3 (often foll. by to + infin.) a thing or person that may be relied on (a certainty to win the Derby). Phrases and idioms for a certainty beyond the possibility of doubt. Etymology: ME f. AF certaint{eacute}, OF -et{eacute} (as CERTAIN)