Sentence:  ...the result of which congress was an unanimous declaration of their forgiveness of a piece of thoughtless levity on the part of the giddy girl ; and every allowance being pleaded for her <WSD>single-heartedness</WSD> and ingenuousness, it was determined that no allusion whatever should again be made to the disagreeable subject; 
Meaning of the word marked with <WSD> tags:  Straightforwardness; lack of duplicity.