ataxia n.

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."

1620s, "science of arranging military forces for combat," from Modern Latin tactica (17c.), from Greek taktike techne "art of arrangement," noun use of fem. of taktikos "of or pertaining to arrangement," especially "tactics in war," adjective to taxis "arrangement, an arranging, the order or disposition of an army, battle array; order, regularity," verbal noun of tassein "arrange," from PIE root *tag- "to touch, handle."

"characterized by ataxia," 1799, from ataxia + -ic.