Sentence:  How many turned around and headed for wherever they came from is not known, but these "<WSD>gobacks</WSD>" or "turnarounds," as many emigrants called them, often complained that there was either little or no grass for their animals or that there was too much cholera or that the Indian threat was too great. 
Meaning of the word marked with <WSD> tags:  An emigrant heading west on the (Oregon Trail) who gave up and turned back to the east.