I believe I can say, with a great degree of confidence, that the Yoruba term òrìṣà is either 1) a loanword, or 2) a doublet from a conservative dialect (more than likely 1). Not only that, but òrìṣà is cognate with ciKam/Egyptian /Hr/ "face; sight" (< *head) and /wrS.w/ "the awakened ones" (with nTr.w determinatives). This is based on regular sound-meaning correspondences between ciKam and Yoruba.
I say that òrìṣà is either a loan or doublet because the sound law for Yoruba and ciKam is that /h/ and h-type sounds in ciKam are "zero" in Yoruba. The /S/ in ciKam interchanges and correspondes with /x/, /X/, and /H/. These sounds are dropped in Yoruba while Yoruba retains /S/ (given as ṣ in Yoruba orthography). Thus:
Yoruba:
orí "head”
rí "to see; find; discover; perceive; behold"; "to be; seem; appear"
arí “one who sees or finds”
ciKam:
Hr "face; sight" [face; sight Wb 3, 125.6-127.14]
HrHr "to guard; to keep" [Andreu/Cauville, RdE 29, 1977, 10; Meeks, AL 77.2819; Lesko, Dictionary II, 135; KoptHWb 569; vgl. EDG 326 f.]
wrS "to guard; to watch" [Pyr 875a; CT I, 287d]
wrS.w "to be awake" [Wb 1, 335.10-18; ONB 493, Anm. 170; vgl. KoptHWb 170]
wrS.w "woken-ones" [Wb 1, 336.11; LGG II, 509]
Yoruba:
õri, orori "sepulcher" (tomb; grave)
ciKam:
HA.t "tomb" [Wb 3, 12.19-21; FCD 160]
Hr.t "tomb; necropolis" [Wb 3, 143.13-19; FCD 175]
xr "tomb; necroppolis" [Wb 3, 323.9-16; FCD 196; Cerny, Community, 4 ff.]
wrs "necropolis" [Meeks, AL 78.1042]
Yoruba:
yọ̀ “rejoice”
ayọ̀ "joy"
õrì, õyì "giddiness"
àríyá "joy; gladness; merriment"
ciKam:
nHrHr "to rejoice"
rHrH "to be glad (of the heart)" [Wb 2, 442.3]
rSw "to rejoice" [Wb 2, 454.1-12; vgl. FCD 153; Lesko, Dictionary II, 71]
rS.w "joy" [Wb 2, 454.13; Lesko, Dictionary, 71; Wilson, Ptol. Lexikon, 592]
rSrS "joy" [Wb 2, 456.5-7; FCD 153]
The semantax in ciKam is that "seeing" is related to "eyes," which are a part of the "head." Thus: head > eyes > see. "Seeing" is the "action of the head." With "seeing" comes "knowing" (being awake). With this said, the word in ciKam /rx/ "to know" is a variant of wrS "to be awake" and Hr "face; sight."
The word orì in Yoruba, meaning "head" and "guardian spirit", is the primary form of the word òrìṣà "head"; "guardian spirits." They are doublets in the language and òrìṣà cannot be analyzed into two words. Also, there is a very low frequency of the r-ṣ consonant sequence in Yoruba, which leads me to believe it is a loan.
The òrìṣà are the wrS.w "awokened ones." As we say in Yoruba:
Ènìyàn ní d' òrìṣà "It is human beings who become òrìṣà."
It is the enlightened or "awakened ones" [those whose eyes are (face is) opened] who become the deified ancestors: i.e., the òrìṣà. In ancient Km.t, the òrìṣà referred to the "guardians" or "watchmen" (sentries "a soldier stationed to keep guard or to control access to a place"). This was applied to one's spirit double in the Yoruba language and the forces of nature. Note as well that in Ifa we speak about one's "warriors," who are a set of òrìṣàs that an initiate receives usually after having received their Elekes. The warriors consist of Eṣu, Ogún, Ochosi and Oṣun. This, however, seems to be a practice more so in the Diaspora and not native to Yorubaland. But the fundamental idea is still there as òrìṣàs are the guardians and watch over human activities. When a parent dies, and becomes an òrìṣà to their children, then they become watchers over the family in the realm of spirit. As the Yoruba saying goes:
òrìṣà bí iyá kò sí "there is no òrìṣà like mother."
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From Wiki:
"An orisha (spelled òrìṣà in the Yoruba language, orichá or orixá in Latin America) is a spirit that reflects one of the manifestations of the Supreme Divinity (Eledumare, Olorun, Olofi) in Yoruba religion.[1] Orisha are said to have existed in the spiritual world, or Astral plane (òrun) or lived as human beings in the planetary world, or physical plane (ayé). Others are said to be humans who are recognized as deities due to extraordinary feats. Many orishas have found their way to most of the New World as a result of the Atlantic slave trade and are now expressed in practices as varied as Santería, Candomblé, Trinidad Orisha, Umbanda, and Oyotunji, among others."
As I said, it could be a doublet. For example, in Egyptian, you have /ra.w/ "sun; day" and /rk/ "time." This is a doublet in ciKam and the older form is /rk/. One dialect kept the older form, while /k/ > /a/ was the sound change primarily. Another example is that the /r/ in Coptic was mainly dropped. However, there are a few words which retained the /r/. So having the fuller form of terms doesn't necessarily mean a loan word. One dialect could have just kept the older form. Now, it could have been a loan in some proto-stage. Will have to check the neighboring languages. But note that orisa "god" (<head) is all across Africa.