Sentence:  Spencer 's potential followers <WSD>were</WSD> openly sullen and morose , missing muster without excuse , expressing in ominous tones their displeasure at the prisoners being kept in irons , communicating with the three by glance and signal . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)