By analogy to other -ητος nouns (ἁγιότης, holiness; ἀδελφότης, brotherhood; βραδύτης, slowness; etc.), θεότης (god-ness) could mean either the quality or nature of being God or a god, or things about or pertaining to God or gods.
The context around its usage in Colossians 2:9 (πᾶν τὸ πλήρωμα τῆς θεότητος, all the fullness of the theotEtos) seems to suggest the meaning God-related stuff, and the fullness being everything one needs to know as regards God.