sceptic
noun
[ ˈskɛptɪk ]
• a person inclined to question or doubt accepted opinions.
• an ancient or modern philosopher who denies the possibility of knowledge, or even rational belief, in some sphere.
sceptic
adjective
• another term for sceptical.
Origin:
late 16th century (in sceptic (sense 2 of the noun)): from French sceptique, or via Latin from Greek skeptikos, from skepsis ‘inquiry, doubt’.