Insist

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late 16th century (in the sense ‘persist, persevere’): from Latin insistere ‘persist’, from in- ‘upon’ + sistere ‘stand’.

wiktionary

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Partly from Middle French insister, from Latin īnsistere; and partly from a back-formation from insistence.

etymonline

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insist (v.)

1580s, from French insister (14c.) or directly from Latin insistere "take a stand, stand on, stand still; follow, pursue; insist, press vigorously, urge, dwell upon," from in- "upon" (from PIE root *en "in") + sistere "take a stand," from PIE *si-st-, reduplicated form of root *sta- "to stand, make or be firm." Perhaps in some cases a back-formation from insistence. Related: Insisted; insisting.