official vs underground

official

noun
  • An office holder, a person holding an official position in government, sports, or other organization. 

adj
  • Discharging an office or function. 

  • Relating to an office; especially, to a subordinate executive officer or attendant. 

  • True, real, beyond doubt. 

  • Approved by authority; authorized. 

  • Of or pertaining to an office or public trust. 

  • Derived from the proper office or officer, or from the proper authority; made or communicated by virtue of authority 

  • Dubious but recognized by authorities as truth and/or canon. 

  • Listed in a national pharmacopeia. 

  • Relating to an ecclesiastical judge appointed by a bishop, chapter, archdeacon, etc., with charge of the spiritual jurisdiction. 

  • Sanctioned by the pharmacopoeia; appointed to be used in medicine; officinal. 

underground

adv
  • Below the ground. 

  • Secretly. 

noun
  • A movement or organisation of people who resist artistic convention. 

  • A movement or organisation of people who resist political convention. 

  • Regions beneath the surface of the earth, both natural (eg. caves) and man-made (eg. mines). 

  • Synonym of subway: a railway that is under the ground. 

verb
  • To route electricity distribution cables underground. 

adj
  • Hidden, furtive, secretive. 

  • Below the ground; below the surface of the Earth. 

  • Outside the mainstream, especially unofficial and hidden from the authorities. 

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