prefix meaning "not, without," from Greek a-, an- "not" (the "alpha privative"), from PIE root *ne- "not" (source also of English un-).

In words from Greek, such as abysmal, adamant, amethyst; also partly nativized as a prefix of negation (asexual, amoral, agnostic). The ancient alpha privatum, denoting want or absence.

Greek also had an alpha copulativum, a- or ha-, expressing union or likeness, which is the a- expressing "together" in acolyte, acoustic, Adelphi, etc. It is from PIE root *sem- (1) "one; as one, together with."

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."

"characterized by debility, weak," 1788, from Latinized form of Greek asthenikos, asthenes "weak, without strength, feeble" (see asthenia).

layer of the Earth's upper mantle, 1914, literally "sphere of weakness" (by comparison with the lithosphere), from Greek asthenes "weak" (see asthenia) + sphere.

"muscular weakness," 1856, medical Latin; see myo- "muscle" + asthenia "weakness." Related: Myasthenic.

"nervous exhaustion," 1854, medical Latin, from neur- (form of neuro- before a vowel) + asthenia "weakness" (see asthenia). Related: Neurasthenic.