ˈsinisternessrare. [f. as prec. + -ness.] The quality of being sinister, in various senses. 1659Gauden Tears Ch. 62 The ignorance,..precipitancy and sinisternesse of their silly censures.1727Bailey (vol. II. ed. 2), Sinisterness, Unfairness, Self-Interestedness [1730 (fol.) adds Aukwardness].