monotonic vs monotonous

monotonic

adj
  • Uttered in a monotone; monotonous. 

  • said of a function that either never decreases or never increases as its independent variable increases. 

  • of or using the Greek system of diacritics which discards the breathings and employs a single accent to indicate stress. It replaced polytonic system in 1982. 

monotonous

adj
  • Tedious, repetitious, or lacking in variety. 

  • Having an unvarying pitch or tone. 

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