the typical ending of the first element of compounds of Greek origin (as -i- is, in compounds of Latin origin), used regularly in forming new compounds with elements of Greek origin and often used in English as a connective irrespective of etymology: Franco-Italian; geography; seriocomic; speedometer.
Origin of -o-
Middle English (< Old French) < Latin < Greek
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Word Origin for -o-
from Greek, stem vowel of many nouns and adjectives in combination
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Used as a connective to join word elements:acidophilic.
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