ab- vs under-

ab-

prefix

  • Away from; outside of. 

  • A unit of electromagnetic charge in the centimeter-gram-second system: the abcoulomb. 

  • From. 

under-

prefix

  • Behind 

  • Beneath, under 

  • Subordinate to 

  • Deficient, below what is correct 

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