Having or characterized by energy; vigorous and forceful (archaic form, rarely used in modern English).
From energic plus the adjectival suffix -al, following the pattern of making Greek adjectives conform to English morphology. This double-suffix form represents an older convention of English word-building that has largely been superseded.
This word is a linguistic fossil showing how English speakers used to stack suffixes (-ic + -al) in ways that would seem redundant today—it's like watching the experimental phase of English grammar before things standardized.
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