asthenic vs lethargic

asthenic

adj

  • Characterized by, or pertaining to, debility; weak; debilitating. 

noun

  • A person who has asthenia. 

lethargic

adj

  • indifferent, apathetic 

  • sluggish, slow 

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