on the level vs plain-speaking

on the level

prep
  • Synonym of on the square (“discreet reference to freemasonry”) 

  • Honest(ly), sincere(ly), straightforward(ly), fair(ly). 

plain-speaking

adj
  • Synonym of plain-spoken 

How often have the words on the level and plain-speaking occurred in a corpus of books? (source: Google Ngram Viewer )