Sentence:  I do n't know whether he was after our <WSD>rider</WSD> , who had gone by a minute before , or whether he was simply scouting conditions ; but when he passed us by , a musket roared , and he reared his horse , swung it around , and began to whip it back in the direction from which he had come . 
Meaning of the word marked with <WSD> tags:  a traveler who actively rides an animal (as a horse or camel)