Sentence:  She imparted these stories gradually to Miss Crawley; gave her the whole benefit of them; felt it to be her <WSD>bounden</WSD> duty as a Christian woman and mother of a family to do so; had not the smallest remorse or compunction for the victim whom her tongue was immolating; nay, very likely thought her act was quite meritorious, and plumed herself upon her resolute manner of performing it. 
Meaning of the word marked with <WSD> tags:  "Now chiefly in the term" '''bounden duty''': made obligatory; binding.