Intense

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late Middle English: from Old French, or from Latin intensus ‘stretched tightly, strained’, past participle of intendere (see intend).

wiktionary

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Borrowed from Middle French intense, from Latin intensus(“stretched tight”), past participle of intendere(“to stretch out”), from in(“in, upon, to”) + tendere(“to stretch”).

etymonline

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intense (adj.)

early 15c., of situations or qualities, "great, extreme," from Old French intense (13c.), from Latin intensus "stretched, strained, high-strung, tight," originally past participle of intendere in its literal sense of "stretch out, strain" (see intend). From 1630s of persons, "high-strung." Related: Intensely; intenseness.