plus if anyone wants to ask how come isildur was floating down a river with arrows in his back when he was clearly seen being jumped on by ORCS (not goblins hehe) well dont because il tell you now to save you the trouble
when the orcs ambushed isildur and his men started to defend, fight back, but there were too many orcs so this man (forgotten his name, must be important though as he orders the king about) tells the king to flee, isildur declines, so he orders him too, so isildur puts on the ring escapes and swims down the river (invisible, orcs apparently dont ask questions such as why is that water splashing over there?) the ring slips off his finger, the orcs realise hes there and arrow him, (instead of going in and killing him to try and get the ring, how could they know hed lost it)
Here's the word from JRR Tolkien himself.
"Orcs (the word is as far as I am concerned actually derived from Old English orc 'demon', but only because of its phonetic suitability) are nowhere clearly stated to be of any particular origin. But since they are servants of the Dark Power, and later of Sauron, neither of whom could, or would, produce living things, the must be 'corruptions'. They are not based on direct experience of mine; but owe, I suppose, a good deal to the goblin tradition (globin is used as a translation in 'The Hobbit', where orc only occurs once, I think), especially as it appears in George MacDonald, except for the soft feet which I never believed in. The name has the form orch (pl. yrch) in Sindarin and uruk in the Black Speech.
--JRR Tolkien, Letter 144
"Your preference of 'goblins' to 'orcs' involves a large question and a matter of taste, and perhaps historical pedantry on my part. Personally I prefer Orcs (since these creatures are not 'goblins', not even the goblins of George MacDonald, which they do to some extent resemble).
--JRR Tolkien, Letter 151
From the looks of these two letters alone, it appears that goblins and orcs are one and the same. It is only a matter of translation to Tolkien. I believe that he states in one of his letters that terms used in the book, such as orc, elf, dwarve, etc., are not the proper names of what he is writing about, but the closest equivalent in our speech. Another good thing to read is "On Translation" in the appendix of ROTK. I'll try to find out some more information if I can.
It probably would've been better for me to include the entirety of the letter, but those quotes both come from letters that are quite long. When Tolkien is writing about Orcs not being goblins, he is not making reference to his works. He is speaking about how he based orcs off of items in other literature. Specifically, he is referring to how the term goblin is used in other literature by other authors, and comparing those characterizations to his own.
As for orcs having no origin, I believe that is also dependent on how you approach the wording. As the quote says, orcs were not created by Melkor or by Sauron. According to the Silmarillion, Orcs began as elves who were put into prison and corrupted through slow acts of cruelty. It was through those acts that those captured elves became orcs. In a way they were created from elves, but they are more a corruption of them. Think about the statement that Darth Vader killed Anakin Skywalker. It was actually the Dark Side that corrupted Anakin and turned into Vader, yet Obi-Wan's original statement would still hold true. I think of it as an extremely severe case of brainwashing.