neurasthenia (n.)

before vowels neur-, word-forming element meaning "pertaining to a nerve or nerves or the nervous system," from Greek neura "nerve" (Galen), originally "sinew, bowstring," also neuron "sinew, string (of a bow or musical instrument); cord; penis;" in plural "strength, vigor," from PIE *(s)neuro- "tendon, sinew" (see nerve (n.)). In Greek, puppets were neurospastos, literally "drawn by strings."

"weakness, debility," 1788, medical Latin, from Greek astheneia "want of strength, weakness, feebleness, sickness; a sickness, a disease," from asthenes "weak, without strength, feeble," from a- "not, without" (see a- (3)) + sthenos "strength, power, ability, might," which is of uncertain origin, perhaps from PIE root *segh- "to have, hold," on the notion of "steadfastness, toughness."

Proto-Indo-European root meaning "to hold."

It forms all or part of: Antioch; asseverate; asthenia; asthenosphere; cachectic; cachexia; calisthenics; cathexis; entelechy; eunuch; epoch; hectic; Hector; ischemia; myasthenia; neurasthenia; Ophiuchus; persevere; schema; schematic; scheme; scholar; scholastic; school (n.1) "place of instruction;" severe; severity; Siegfried.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sahate "he masters, overcomes," sahah "power, victory;" Avestan hazah "power, victory;" Greek skhema "figure, appearance, the nature of a thing," related to skhein "to get," ekhein "to have, hold; be in a given state or condition;" Gothic sigis, Old High German sigu, Old Norse sigr, Old English sige "victory."