atresia 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."

*terə-, Proto-Indo-European root meaning "to rub, turn," with derivatives referring to twisting, also to boring, drilling, piercing; and to the rubbing of cereal grain to remove the husks, and thus to threshing.

It forms all or part of: atresia; attorn; attorney; attrition; contour; contrite; detour; detriment; diatribe; drill (v.) "bore a hole;" lithotripsy; return; septentrion; thrash; thread; thresh; throw; threshold; trauma; trepan; tribadism; tribology; tribulation; trite; triticale; triturate; trout; trypsin; tryptophan; turn.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit turah "wounded, hurt;" Greek teirein "to rub, rub away;" Latin terere "to rub, thresh, grind, wear away," tornus "turning lathe;" Old Church Slavonic tiro "to rub;" Lithuanian trinu, trinti "to rub," Old Irish tarathar "borer," Welsh taraw "to strike."