non- vs ob-

non-

prefix
  • Used in the sense of no or none, to show lack of or failure to perform; or in the sense of not, to negate the meaning of the word to which it is prefixed. 

  • prevocalic form of nona- 

ob-

prefix
  • Obligatory; prepended to the name of a topic being mentioned to avoid accusations of being off-topic. 

  • Of a reversed shape. 

  • Against; facing; a combining prefix found in verbs of Latin origin. 

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