Skeptical

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late 16th century (in sceptic (sense 2 of the noun)): from French sceptique, or via Latin from Greek skeptikos, from skepsis ‘inquiry, doubt’.

wiktionary

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skeptic +‎  -al

etymonline

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skeptical (adj.)

also sceptical, 1630s; see skeptic + -al (1). Related: Skeptically.