One who is yet undecided as to what is true; one who is looking or inquiring for what is true; an inquirer after facts or reasons.
A doubter as to whether any fact or truth can be certainly known; a universal doubter; a Pyrrhonist; hence, in modern usage, occasionally, a person who questions whether any truth or fact can be established on philosophical grounds; sometimes, a critical inquirer, in opposition to a dogmatist.
A person who doubts the existence and perfections of God, or the truth of revelation; one who disbelieves the divine origin of the Christian religion.
Everyone - pantheist, atheist, skeptic, polytheist - has to answer these questions: 'Where did I come from? What is life's meaning? How do I define right from wrong and what happens to me when I die?' Those are the fulcrum points of our existence. Ravi Zacharias
Scientists are skeptics. It's unfortunate that the word 'skeptic' has taken on other connotations in the culture involving nihilism and cynicism. Really, in its pure and original meaning, it's just thoughtful inquiry. Michael Shermer