Theta
According to Porphyry of Tyros, the Egyptians used an X within a circle as a symbol of the soul; having a value of nine, it was used as a symbol for Ennead.
The Ennead or Great Ennead was a group of nine deities in Egyptian mythology worshipped at Heliopolis: the sun god Atum; his children Shu and Tefnut; their children Geb and Nut; and their children Osiris, Isis, Set, and Nephthys.[1] The Ennead sometimes includes Horus the Elder, an ancient form of the falcon god, not the son of Osiris and Isis.
Status within ancient Egypt
The Great Ennead was only one of several such groupings of nine deities in ancient Egypt. Its claims to preeminence by its Heliopolitan priests were not respected throughout Egypt.[2] As close as Memphis (also within modern Cairo), the priests of Ptah celebrated him as superior to the Nine.[2]
In addition to Memphis having its own creation myth, the Ogdoad (of the city of Hermopolis) centered around physical creation and eight primordial gods was another creation story that existed at the same time.[2]
Name in Egyptian, Greek, and Latin
|
|  |  |  | psḏt | |||
|---|---|---|---|---|---|---|---|---|
The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs | The Ennead[3](p 2464) in hieroglyphs |
The English name ennead is a borrowing via Latin of the Greek name enneás (ἐννεάς), meaning "the nine".[4] The term was a calque of the Egyptian name, written psḏt and also meaning "the Nine". Its original pronunciation is uncertain, since hieroglyphs do not record vowels, but may have been /piˈsiːcʼat/ in Old Egyptian, /piˈsiːtʼaʔ/ in Middle Egyptian, and /pəˈsiːtʼə/ in Late Egyptian. Egyptologists conventionally transcribe it as Pesedjet.
Johannes Lydus says that the Egyptians used a symbol for Kosmos in the form of theta, with a fiery circle representing the world, and a snake spanning the middle representing Agathos Daimon (literally: good spirit).[5]
Theta (UK: /ˈθiːtə/, US: /ˈθeɪtə/; uppercase: Θ or ϴ; lowercase: θ[note ^1] or ϑ;
Ancient Greek: θῆτα thē̂ta [tʰɛ̂ːta];
Modern: θήτα thī́ta [ˈθita]) is the eighth letter of the Greek alphabet,
derived from the Phoenician letter Teth 
.
In the system of Greek numerals, it has a value of 9.
Greek
The alphabet on a black figure vessel, with a point-and-circle theta
In Ancient Greek, θ represented the aspirated voiceless dental plosive IPA: [t̪ʰ], but in Modern Greek it represents the voiceless dental fricative IPA: [θ].
Forms
In its archaic form, θ was written as a cross within a circle (as in the Etruscan 
or 
), and later, as a line or point in circle (
or 
).
The cursive form ϑ was retained by Unicode as U+03D1 ϑ GREEK THETA SYMBOL, separate from U+03B8 θ GREEK SMALL LETTER THETA. (There is also U+03F4 ϴ GREEK CAPITAL THETA SYMBOL).
For the purpose of writing Greek text, the two can be font variants of a single character, but θ and ϑ are also used as distinct symbols in technical and mathematical contexts.
Extensive lists of examples follow below at Mathematics and Science. U+03D1 ϑ GREEK THETA SYMBOL (script theta) is also common in biblical and theological usage
e.g. πρόϑεσις instead of πρόθεσις (means placing in public or laying out a corpse).