The Old English word commonly cited as a source for Tolkien’s “orc” is orcneas.
The term appears in the Old English poem Beowulf, in a passage describing monstrous beings descended from Cain. Tolkien was a specialist in Old English and knew the poem’s language intimately, making the connection especially significant for readers studying the origins of his vocabulary.
In Middle-earth, orcs are hostile humanoid creatures associated with the armies of Morgoth and Sauron. Tolkien also used the spelling “Orc,” and his languages and explanatory notes connect the word with older Germanic forms such as Old English orc.
The word is sometimes incorrectly treated as an invention with no earlier linguistic history. Tolkien did create a distinctive fictional meaning and mythology around orcs, but the form drew on real medieval language. “Wyrd,” “middangeard,” and “eorþe” are also Old English words, yet they are not the specific source commonly cited for this term.