Simile is where a comparison between two things is made for effect. "He was as tough as teak."
"She was as pretty as a picture" (although that depends on the picture I guess).
Solitary Reaper is written in very flowery language anyway (and I'm surprised you have been asked to analyse it - such stuff was considered old-fashioned even when I was a school).
Anyway, look for lines (I think there are actually two) that demonstrate a comparison similar to the examples.