Etymology
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azo- 
before vowels az-, word-forming element denoting the presence of nitrogen, used from late 19c. as combining form of azote (1791), the old term for "nitrogen" (from Greek a- "not, without" (see a- (3)) + zoion "a living being," from PIE root *gwei- "to live"), which was coined in French by Lavoisier & de Morveau because living things cannot survive in the pure gas.
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gastro- 

also gastero-, before vowels gastr-, scientific word-forming element meaning "stomach," from Greek gastro-, combining form of gaster (genitive gastros) "belly, paunch; womb" (see gastric). Also used in compounds in ancient Greek, as gastrobarys "heavy with child."

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