noun

• (medicine) Weakness; loss of strength.
  "The savage gets a headache when his thought is forced to flow in a stream of representation. In the imbecile, in the idiot we find the same thing manifested. They can only think in concrete sensory terms. In mental asthenia which approaches the state of the higher stages of imbecility and also in secondary dementia, states consequent on psychic degeneration, we find the same truth illustrated. The patient's mental activity falls many stages nearer to the level of presentative life. It is only in the higher forms of psychic life that representative elements become free, independent, and are freely and easily associated and dissociated."
• (figurative) weakness
  "You see nothing that might even remotely suggest life, beyond the solitary brave watering the ponies below you; but that is because the asthenia of civilization has left you half blind as well as half deaf, for where you see nothing and hear nothing Geronimo is conscious of life, movement and sound-of rodents, reptiles and birds awaiting, quiescent, the lessening heat of dusk."