Orc is from Old English orcneas, which appears in the epic poem Beowulf, and refers to one of the races who are called the offspring of Cain during the initial description of Grendel ("Þanon untydras ealle onwocon,/eotenas ond ylfe, ond orcneas," ll. 111-112). In a letter of 1954 Tolkien gave orc as "demon" and claimed he used the word because of its "phonetic suitability" — its similarity to various equivalent terms in his Middle-earth languages. In an essay on Elven languages, written in 1954, Tolkien gives meaning of 'orc' as "evil spirit or bogey" and goes on to state that the origin of the Old English word is the Latin name Orcus — god of the underworld.http://en.wikipedia.org/wiki/Orc_(Middle-earth
About the goblins of The Hobbit, Tolkien wrote:
"They are not based on direct experience of mine; but owe, I suppose, a good deal to the goblin tradition ... especially as it appears in George MacDonald, except for the soft feet which I never believed in."
Middle-earth terms for OrcsIn the High-elven tongue Quenya, the word for "Orc" was urco, plural urqui, meaning "bogey", or "bogeyman", that is, something that provokes fear. In the Grey-elven tongue Sindarin, it was orch, plural yrch. In the Dwarven tongue Khuzdul, it was rukhs, plural rakhâs. In the language of the Drúedain or Wild Men, it was gorgûn. In the Black Speech of Mordor, the equivalent was Uruk, as can be seen in Uruk-hai, "Orc-folk". Orc itself is from Rohirric and the Hobbit-language, which shared linguistic roots, but the term is clearly related to the older Elvish words.
Uruk and Uruk-hai were reserved for the Uruks themselves, a special breed or breeds of Orc; they called smaller, weaker Orcs snaga, "slave". The Grey Elves also referred to the Orcs as a whole as the Glamhoth, "noisy horde". The word "goblin" is used to represent the original Hobbit Orc. In The History of Middle-earth Tolkien writes about an Orc captain named Boldog but later specifies that Boldog may have been either a term or a title for another special kind of Orc instead of a personal name.