Reptilian

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late Middle English: from late Latin, neuter of reptilis, from Latin rept- ‘crawled’, from the verb repere .

wiktionary

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From reptile +‎ -ian, replacing earlier reptilious and adjectival reptile.

etymonline

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reptilian (adj.)

"of, resembling, or characteristic of reptiles," 1835, from reptile + -ian. Transferred meaning "malignant, cold, underhanded" is by 1859.