Sentence:  Act, as we have already emphasized, is also called by Aristotle an <WSD>entelechy</WSD>. ... [A]ct and <WSD>entelechy</WSD> bespeak something fulfilled, actualized perfection, or the actualized. The soul, hence, insofar as it is essence or form of the body, is the act and <WSD>entelechy</WSD> of the body; and in general all forms of sensible substances are act and <WSD>entelechy</WSD>. God, we will see, will be pure <WSD>entelechy</WSD> (and just as the other movent Intelligences of the celestial spheres). 
Meaning of the word marked with <WSD> tags:  The complete realisation and final form of some potential concept or function; the conditions under which a potential thing becomes actualized.