Sentence:  Youngish man on the make , Madden labeled him , and was ready to guess that in a correct , not too pushing fashion , the junior <WSD>partner</WSD> of the firm had political ambitions ; that Mrs. Garth would be impeccably suitable as the wife of a rising young lawyer ; that there were three children , two boys and a girl ; that she was active in the Woman 's Club and he in Lions , Rotary , and Jaycee ; and finally , that neither of them had harbored an unorthodox opinion since their wedding day . 
Meaning of the word marked with <WSD> tags:  an associate in an activity or endeavor or sphere of common interest