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.
Being a skeptic just means being rational and empirical: thinking and seeing before believing. Michael Shermer
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
Preaching is to much avail, but practice is far more effective. A godly life is the strongest argument you can offer the skeptic. Hosea Ballou
The fact that a believer is happier than a skeptic is no more to the point than the fact that a drunken man is happier than a sober one. George Bernard Shaw