Sentence:  Rumors of the offer Tom Horn had made at the <WSD>Stockgrowers'</WSD> Association meeting had leaked out by then , and as a grand jury investigation of the murder got underway , the prosecuting attorney , a Colonel Baird , ordered that the tall stock detective be summoned for questioning . 
Meaning of the word marked with <WSD> tags:  any number of entities (members) considered as a unit