fatigue vs relaxation

fatigue

verb
  • To tire or make weary by physical or mental exertion. 

  • To lose so much strength or energy that one becomes tired, weary, feeble or exhausted. 

  • To cause to undergo the process of fatigue. 

  • To wilt a salad by dressing or tossing it. 

  • To undergo the process of fatigue; to fail as a result of fatigue. 

noun
  • Weakening and eventual failure of material, typically by cracking leading to complete separation, caused by repeated application of mechanical stress to the material. 

  • A weariness caused by exertion; exhaustion. 

  • A menial task or tasks, especially in the military. 

relaxation

noun
  • The transition of a nucleus, atom or molecule from a higher energy level to a lower one; the opposite of excitation 

  • The release following musical tension. 

  • A diminution of tone, tension, or firmness; specifically in pathology: a looseness; a diminution of the natural and healthy tone of parts. 

  • Remission of attention or application. 

  • The act of relaxing or the state of being relaxed; the opposite of stress or tension; the aim of recreation and leisure activities. 

  • Unbending; recreation; a state or occupation intended to give mental or bodily relief after effort. 

  • Remission or abatement of rigor. 

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