[-o-] [ME, fr. OF, fr. L, fr. Gk, thematic vowel of many nouns and adjectives in combination]--used as a connective vowel orig. to join word elements of Greek origin and now also to join word elements of Latin or other origin "speedometer" "elastomer"
-O-
Meaning of -O- in English
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012