The root of Selene is thought to be σέλας
(selas):
https://en.wiktionary.org/wiki/Σελήνη#Ancient_Greek
I wish Pavlos were still around: he was a native Greek and therefore perfectly suited to answer questions like yours.
Now that I think of it... if all else fails, you could try going to
/r/AncientGreek and
/r/Greek on Reddit (or even
/r/Greece). There should be native Greeks there that can answer your questions better than we can.
• Ancient Greek:
https://old.reddit.com/r/AncientGreek/
• Greek:
https://old.reddit.com/r/GREEK/
• Greece:
https://old.reddit.com/r/greece/
Forchta in biuonga quamon ouer mi, in bethecoda mi thuisternussi.
In ic quad: "uuie sal geuan mi fetheron also duuon, in ic fliugon sal in raston sal?"