Of, relating to, or derived from energy; full of energy or exhibiting vigorous action.
From Greek 'energetikos' (active, vigorous) based on 'energeia' plus '-cal' (variant of '-al'). The suffix '-cal' often appears in place of simple '-al' for certain adjectives.
English has multiple ways to say the same thing—'energetic,' 'energetical,' and 'energetick' (archaic) all existed, but 'energetic' won out, probably because it's shorter and easier to say.
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