EO

1.
executive order.
1.
a combining form meaning “early,” “primeval,” used in the formation of compound words:
Eocene; eohippus.
1.
ex officio.
[ey-oh ip-soh; English ee-oh ip-soh] /ˈeɪ oʊ ˈɪp soʊ; English ˈi oʊ ˈɪp soʊ/
adverb, Latin.
1.
by that very fact.
[ey-oh noh-mi-ne; English ee-oh nom-i-nee] /ˈeɪ oʊ ˈnoʊ mɪˌnɛ; English ˈi oʊ ˈnɒm ɪ ni/
adverb, Latin.
1.
by that name.
combining form
1.
early or primeval: Eocene, eohippus
abbreviation
1.
ex officio

word-forming element used from mid-19c. (first in Eocene) in compound words formed by earth-scientists and meaning “characterized by the earliest appearance of,” from Greek eos “dawn,” from PIE *aus-, cognate with Modern English east (q.v.). Piltdown Man, before exposed as a fraud, was known as Eoanthropus.
Esperanto
1.
ethylene oxide
2.
executive order
Latin ex officio (by virtue of office)