"Ο σκεπτικιστής φιλόσοφος."

Translation: The sceptical philosopher.

[EndlessOrbitSSX]

Wouldn't "ο σκεπτικός φιλόσοφος" be a better match?

[jaye16]

Yes, that is another sentence. There is a difference: σκεπτικός means someone who doubts a fact/statement etc while ο σκεπτικιστης is a follower of a branch of philosophy by that name which as its name says involves "disbelieving". http://www.thefreedictionary.com/Skeptics So, both, of course, are correct.

[Marva441926]

Jaye, this distinction exists in English as well. Someone who is sceptical [adjective] of something is disbelieving/doubtful of it. Someone who is a skeptic [noun] is a follower of Skepticism. (I have heard people use "skepticist" to mean the latter as well, but I think it's redundant and, for what it's worth, my spell-checker doesn't like it either.)

[annamerku]

yes, you are right. The translation is wrong

[I.Schmidt1]

Am I right, that here are two nouns, because I can not find an adjective "σκεπτικιστής".
if there is one, can someone please tell me how it is declined?

[troll1995]

There are two nouns, as you said. Σκεπτικιστής works as a attribute in this sentence. It is declined as

Nominative: ο σκεπτικιστής
Genitive: του σκεπτικιστή
Accusative: τον σκεπτικιστή
Vocative: (-) σκεπτικιστή