Sentence:  All wore a costume suggestive of a more tranquil and prosperous age than this — Dame Clara Butt singing, in a voice not quite so deep as Arumugam's, 'Land of Hope and Glory', the gold squeezed from tropical <WSD>helots</WSD> enhancing the upper-class comforts of a cold climate. 
Meaning of the word marked with <WSD> tags:  A serf; a slave.