Where does “energetic” come from?

Energetic comes from New Latin energeticus, meaning "active" or "operative."

energetic (English): Possessing or pertaining to energy; Characterised...

Definitions

energetic traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	French	énergétique	related to energy
2	Ancient Greek	ἐνεργητικός	Able to act on; acting on; Active; In the active...
3	Ancient Greek	ἐνεργέω	to be in action or activity, to operate; to...
4	Ancient Greek	ἐνεργός	at work, active
5	Ancient Greek	ἐν-	in, within; on
6	Ancient Greek	ἐν	in, on, at; among; in, at, or during the time of
7	Ancient Greek	δέρμα	skin, hide
8	Ancient Greek	γλυφή	carving, carved work; hole cut
9	Ancient Greek	-ῐ́ᾱ	{{l\|en\|-ia}}; "suffix forming abstract feminine...
10	Proto-Indo-European	-íh₂	—
11	Proto-Indo-European	-h₂	Creates collective nouns, which refer to groups...

Step	Language	Word	Meaning
1	New Latin	energeticus	—