above-board vs essential

above-board

adj
  • In open sight; without trick, concealment, or deception. 

adv
  • Honestly; openly. 

essential

adj
  • Having the nature of essence; not physical. 

  • Necessary. 

  • Necessary for survival but not synthesized by the organism, thus needing to be ingested. 

  • Being in the basic form; showing its essence. 

  • Really existing; existent. 

  • Very important; of high importance. 

  • Such that each complementary region is irreducible, the boundary of each complementary region is incompressible by disks and monogons in the complementary region, and no leaf is a sphere or a torus bounding a solid torus in the manifold. 

  • Idiopathic. 

noun
  • A necessary ingredient. 

  • A fundamental ingredient. 

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