noun

• (agriculture) An implement having a semicircular blade and short handle, used for cutting long grass and cereal crops.
  "Coordinate term: scythe"
• Anything resembling a sickle, especially:
  "Then, ere the silver sickle of that month Became her golden shield, I stole from court With Cyril and with Florian, unperceived."

verb

• (agriculture, transitive, rare) To cut with a sickle.
  "Near-synonyms: reap, mow"
• (pathology, intransitive) Of red blood cells: to assume an abnormal crescent shape.
  "Even the cells of heterozygotes will sickle if the oxygen tension is low enough."
• (pathology, transitive) To deform (as with a red blood cell) into an abnormal crescent shape, to cause to sickle.