Sentence:  Those named in the Greek paper were manufacturing reasons to steal aft under pretence of some call of <WSD>duty</WSD> , so as to be near Spencer , watching an opportunity to communicate with him . 
Meaning of the word marked with <WSD> tags:  the social force that binds you to the courses of action demanded by that force; every opportunity, an obligation; every possession, a duty"- John D.Rockefeller Jr