incurvate vs sigmoid

incurvate

adj
  • Curved; bent; crooked. 

  • bending inwards. 

verb
  • to have a curved or bent shape; to bend or curve inwards. 

  • To bend (especially inwards); to give a curved shape to. 

sigmoid

adj
  • Curved in two directions, like the letter "S", or the Greek ς (sigma); having a serpentine shape. 

  • Relating to the sigmoid colon. 

  • Exhibiting logistic growth; having a graph that accelerates until it reaches a carrying capacity. 

How often have the words incurvate and sigmoid occurred in a corpus of books? (source: Google Ngram Viewer )