yelwa (1) adj. "loathsome" (DYEL; according to VT45:11, Tolkien changed this word from yelva.)
This word was adapted from its Sindarin cognate orch, since the Noldor did not encounter orcs until they returned to Middle Earth (WJ/390). There are two attested plurals for this word, orqui and orcor. One possible scenario is that the word was at first treated as a u-stem noun by analogy with urco (urcu-), but later as the two words were disassociated, the declension of orco was regularized and treated as an ordinary vocalic noun.
This is the theory followed here, so that orcor is considered the regular plural and orqui archaic, probably active only in the First Age. If you use the orqui plural, you should also treat this as a u-stem noun (orcu-). @@@
orco ("k") noun "Orc", pl. orcor or orqui (WJ:390, ÓROK; pl. Orcor also in WJ:12, MR:74, 194). If the pl. form orqui is preferred, the word should be assigned the stem-form orcu-. Early "Qenya" has orc ("k") (orqu-) ("q") "monster, demon" (LT1:264; in LotR-style Quenya, no word can end in -rc.)
urco ("k"), stem *urcu- and pl. urqui, noun: an old word used in the lore of the Blessed Realm for anything that caused fear to the Elves during the March; by the Exiled Noldor the word was recognized as the cognate of Sindarin orch and used to mean "Orc". The Sindarin-influenced form orco was also used. (WJ:390)