mega- vs under-

mega-

prefix
  • Very large, great. 

  • Really, very, uber-, super-. 

  • In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by one million (10⁶.) SI Symbol: M. 

  • Multiplying the unit to which it is attached by 2¹³ × 5³ (= 1,024,000, the binary round number closest to a million). 

  • Multiplying the unit to which it is attached by 2²⁰ (= 1,048,576, the binary number closest to a million). Computing symbol: Mi. 

under-

prefix
  • Behind 

  • Beneath, under 

  • Subordinate to 

  • Deficient, below what is correct 

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