Gorman offers the following definition of theosis as it applies to the thought of St. Paul:
Theosis is transformative participation in the kenotic, cruciform character and life of God through Spirit-enabled conformity to the incarnate, crucified, and resurrected/glorified Christ, who is the image of God. (p. 125)
The only thing I might tweak here would be to replace “Spirit-enabled” with “Spirit-actualized” or something of that nature. Other than that this seems to be a good definition of theosis, which makes clear that theosis is not about having our human nature changed into divine nature or something like that. Rather it is transformative participation that results in conformitas Christi.