ophidian vs viperous

ophidian

adj
  • Of or pertaining to the suborder Serpentes; of, related to, or characteristic of a snake or serpent. 

noun
  • Any species of the suborder Serpentes; a snake or serpent. 

viperous

adj
  • of or pertaining to a viper 

  • venomous, malicious or treacherous 

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