The name Orc

[Guinevere]

"Orc" is an old Anglo Saxon word and has nothing to do with Greek!
May I quote a passage from " Tolkien, Author of the century", by Tom Shippey (who is also a Philologist, like Tolkien was)

Tolkien had used the word "orc" in The Hobbit, but his regular word at that point was "goblin". As he built up the linguistic correspondences of Middle-earth, this came to seem out of place, it is a relatively late word in English.(....) Tolkien preferred an Old English word, and found it in two compounds, the plural form "orc-neas" found in BEOWULF, where it seems to mean " demon-corpses", and the singular "orc-thyrs", where the second half is found also in Old Norse and means something like "giant". Demons, giants, zombies - it seems that literate Anglo-Saxons really had very little idea what orcs were at all (...) The word was floating freely, with ominous suggestions but no clear reference. Tolkien took the word, brought the concept into clear focus in detailed scenes, and, as with hobbits, has in a way made both word and thing now canonical.

It's the same with Ents and Wood-woses , these are also AngloSaxon words whose meaning isn't very clear at all. Tolkien seems to have asked himself what might be behind them, and made of them the Ents and wild woodmen in LotR.