languor vs lethargy

languor

noun
  • Dullness, sluggishness; lack of vigour; stagnation. 

  • A state of the body or mind caused by exhaustion or disease and characterized by a languid or weary feeling; lassitude; (countable) an instance of this. 

  • Listless indolence or inactivity, especially if enjoyable or relaxing; dreaminess; (countable) an instance of this. 

  • Heavy humidity and stillness of the air. 

  • Melancholy caused by lovesickness, sadness, etc.; (countable) an instance of this. 

verb
  • To languish. 

lethargy

noun
  • A state of extreme torpor or apathy, especially with lack of emotion, energy or enthusiasm; (loosely) sluggishness, laziness. 

  • A condition characterized by extreme fatigue or drowsiness, deep unresponsiveness, or prolonged sleep patterns. 

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