incognito vs under the radar

incognito

adv
  • Without revealing one's identity. 

noun
  • The assumption of disguise or of a feigned character; the state of being in disguise or not recognized. 

  • One unknown or in disguise, or under an assumed character or name. 

adj
  • Without being known; in an assumed character, or under an assumed title; in disguise. 

under the radar

prep
  • Without attracting notice; in an undetected or secretive manner. 

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