Don How does tagathon relate to telos?
In connotation. Tagathon ταγαθον is ultimately simply "good" agathon with the definite article "the" added to the front: t + agathon = "The Good". As opposed to agathon "a good, good (adjective)"
They're basically referring, I think, to the same thing: that to which all other things point; the ultimate reason why we do what we do.