the mind > mental capacity > knowledge > conformity with what is known, truth > sincerity, freedom from deceit > [noun]
1642 H. More Interpr. Unusuall Names sig. Q3v Monocardia,..single-heartednesse.
1837 T. Hook I. i. 29 The sincerity and single-heartedness of one of the purest, gentlest Nora Creenas that ever walked.