In terminology, theos, from the Greek “Θεο” (theo), god, means “gods”, which derives from the Greek letter Theta ‘Θ’ (see: alphabet), representing, numerically, the Greek number “9”, symbolic of the nine gods (paut) of the Ennead (Porphyry, c.280) of Heliopolis; theta, itself, derived from Egyptian circle with X inside "⊗", also called the ‘tet’ or ‘teth’ symbol in Phoenician (1050BC) and ‘+’ sign in circle “⊕” in Etruscan (300BC), each, in turn, being the symbol for the ancient city of Heliopolis (2800BC), or, in the form of a circle with dot inside " ʘ ", the symbol for Ra, the supreme sun god of Egypt (Gardiner, 1929), who, in the form of Atum-Ra, was the original creator god of the Ennead, i.e. the first of the nine god group (paut) of the Heliopolis creation myth; also said to derive from the Ouroboros, representative of the symbol of the cosmos or universe (Lydus, 555).

In 800BC, Hesiod penned his Theogony , or Θεο-γονία (Theo-gony), a term meaning “generation of the gods”, wherein, after studying the creation myths of Egypt (see: Egyptian pantheon), penned a more anthropomorphized, god reduced, version for the Greeks to read (see: Greek pantheon), basically a rescript of the former.

In 375BC, Plato, in his Republic, introduced the term “theologia”, from theo- meaning “god” + -logos meaning “speech or words”, + -ia meaning “names of actions and abstract things”, meaning “speech or words about god, gods, or god-like things” (Naddaf, 1995). [1]

In 350BC, Aristotle, in his Metaphysics (Ѻ), following digression on his theory of “actuality” (entelecheia, Greek: ἐντελέχεια) and “potentiality” (dynamis, Greek: δύναμις), where the former is perfection, realization, fullness of being, the latter is imperfection, incompleteness, perfectibility – former is the determining, the latter the determinable principle – delves into his ideas on “theologia”.

The term “theology”, following the work of Marcus Varro (c.40BC), Eusebius (c.320), and Augustine (c.400), eventually came to be known as the study of god or gods.

The following are related quotes:

Theologia first appears in Plato, and the term is used both by him (Republic, 379a) and by Aristotle (Metaphysics, 1000a, 1071b) to designate the activity of the poets who gave cosmogonical accounts. Aristotle particularly uses it in contrast with the philosophical speculations of the physikoi (e.g. Metaphysics, 1075b); in effect, it is parallel to the distinction between mythos and logos (qq.v.). In Metaphysics (1026a), a sharply distinct meaning emerges. Aristotle had divided the theoretical sciences into three classes, of which the third deals with substances that are ‘separate’ (for the sense, see choriston) and without kinesis; this is the ‘first philosophy’ or theologike, so called because such substances are the realm of divinity. Theology later expanded to once again embrace all discourse about the gods, and this new understanding of its scope may be seen in the division of theology into ‘mythical, physical, and political’, a division originating in the Middle Stoa (see Augustine, De civ. Dei VI, 5, citing Varro; compare, ibid. IV, 27 and Eusebius, Praep. Evang. IV, 1).”
— Francis Peters (1967), Greek Philosophical Terms (pg. 194)

1. Naddaf, Gerard. (1995). “Plato’s ‘Theologia’ Revisited” (pdf), SAGP Meeting New York, Dec 28.

External links
Theos – Wikipedia.
theos – Wiktionary.

TDics icon ns