Etymology
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aetio- 
word-forming element used in chemistry and indicating "a fundamental degradation product of a complex organic compound" [Flood], from Latinized combining form of Greek aitia "a cause, an origin" (see etiology). In older, general use it has been reduced in English to etio- (see æ (1)).
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trans- 

word-forming element meaning "across, beyond, through, on the other side of, to go beyond," from Latin trans (prep.) "across, over, beyond," perhaps originally present participle of a verb *trare-, meaning "to cross," from PIE *tra-, variant of root *tere- (2) "cross over, pass through, overcome." In chemical use indicating "a compound in which two characteristic groups are situated on opposite sides of an axis of a molecule" [Flood].

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